ESS Tech (GWH) 10-Q 12 May 22 2022 Q1 Quarterly report Financial data

Cover

Cover - shares	3 Months Ended
	Mar. 31, 2022	May 09, 2022
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2022
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-39525
Entity Registrant Name	ESS Tech, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	98-1550150
Entity Address, Address Line One	26440 SW Parkway Ave.
Entity Address, Address Line Two	Bldg. 83
Entity Address, City or Town	Wilsonville
Entity Address, State or Province	OR
Entity Address, Postal Zip Code	97070
City Area Code	855
Local Phone Number	423-9920
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		152,654,728
Entity Central Index Key	0001819438
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q1
Amendment Flag	false
Common Stock
Entity Information [Line Items]
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	GWH
Security Exchange Name	NYSE
Common Stock Warrants
Entity Information [Line Items]
Title of 12(b) Security	Warrants, each whole warrant exercisable for one share of common stock at an exercise price of $11.50
Trading Symbol	GWH.W
Security Exchange Name	NYSE

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 212,331	$ 238,940
Restricted cash, current	1,167	1,217
Accounts receivable, net	2,928	517
Prepaid expenses and other current assets	4,406	4,844
Total current assets	220,832	245,518
Property and equipment, net	10,056	4,501
Operating lease right-of-use assets	4,260	0
Restricted cash, non-current	75	75
Other non-current assets	261	105
Total assets	235,484	250,199
Current liabilities:
Accounts payable	1,745	1,572
Accrued and other current liabilities	6,615	6,487
Operating lease liabilities, current	1,310	0
Deferred revenue	6,859	3,663
Notes payable, current	1,817	1,900
Total current liabilities	18,346	13,622
Notes payable, non-current	1,483	1,869
Operating lease liabilities, non-current	3,612	0
Earnout warrant liabilities	636	1,476
Public warrant liabilities	8,042	18,666
Private warrant liabilities	3,815	8,855
Other non-current liabilities	101	552
Total liabilities	36,035	45,040
Commitments and contingencies (Note 10)
Stockholders’ equity:
Preferred stock ($0.0001 par value; 200,000,000 shares authorized, none issued and outstanding as of March 31, 2022 and December 31, 2021)	0	0
Common stock ($0.0001 par value; 2,000,000,000 shares authorized, 152,606,563 and 151,839,058 shares issued and outstanding as of March 31, 2022 and December 31, 2021, respectively)	16	16
Additional paid-in capital	745,752	745,753
Accumulated deficit	(546,319)	(540,610)
Total stockholders' equity	199,449	205,159
Total liabilities and stockholders’ equity	$ 235,484	$ 250,199

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Preferred stock, par value (in USD per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	200,000,000	200,000,000
Preferred stock, shares outstanding (in shares)	0	0
Preferred stock, shares issued (in shares)	0	0
Common stock, par value (in USD per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	2,000,000,000	2,000,000,000
Common stock, shares issued (in shares)	152,606,563	151,839,058
Common stock, shares outstanding (in shares)	152,606,563	151,839,058

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Operating expenses:
Research and development	$ 12,898	$ 5,652
Sales and marketing	1,501	512
General and administrative	7,789	2,120
Total operating expenses	22,188	8,284
Loss from operations	(22,188)	(8,284)
Other income (expenses), net:
Interest expense, net	(29)	(57)
Gain (loss) on revaluation of warrant liabilities	15,664	(8,426)
Loss on revaluation of derivative liabilities	0	(138,141)
Gain on revaluation of earnout liabilities	840	0
Other income (expense), net	4	(10)
Total other income (expenses), net	16,479	(146,634)
Net loss to common stockholders	$ (5,709)	$ (154,918)
Net loss per share, basic (in USD per share)	$ (0.04)	$ (2.51)
Net loss per share, diluted (in USD per share)	$ (0.04)	$ (2.51)
Weighted average shares used in per share calculation, basic (in shares)	151,683,819	61,693,067
Weighted average shares used in per share calculation, diluted (in shares)	151,683,819	61,693,067

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock	Common Stock Warrants	Additional Paid-In Capital	Accumulated Deficit
Balance at beginning of period (in shares) at Dec. 31, 2020	0
Balance at beginning of period at Dec. 31, 2020	$ 0
Balance at end of period (in shares) at Mar. 31, 2021	0
Balance at end of period at Mar. 31, 2021	$ 0
Balance at beginning of period (in shares) at Dec. 31, 2020		58,919,345
Balance at beginning of period at Dec. 31, 2020	(27,888)	$ 6	$ 153	$ 35,446	$ (63,493)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of Legacy ESS Redeemable Convertible Preferred Stock (in shares)		5,746,003
Issuance of Legacy ESS Redeemable Convertible Preferred Stock	29,516	$ 1		29,515
Issuance of common stock upon exercise of options (in shares)		2,379,260
Issuance of common stock upon exercise of options	518			518
Issuance of common stock upon exercise of warrants (in shares)		60,418
Issuance of common stock upon exercise of warrants	356			356
Stock-based compensation expense	129			129
Net loss	(154,918)
Balance at end of period (in shares) at Mar. 31, 2021		67,105,026
Balance at end of period at Mar. 31, 2021	$ (152,287)	$ 7	153	65,964	(218,411)
Balance at beginning of period (in shares) at Dec. 31, 2021	0
Balance at beginning of period at Dec. 31, 2021	$ 0
Balance at end of period (in shares) at Mar. 31, 2022	0
Balance at end of period at Mar. 31, 2022	$ 0
Balance at beginning of period (in shares) at Dec. 31, 2021		151,839,058
Balance at beginning of period at Dec. 31, 2021	$ 205,159	$ 16	0	745,753	(540,610)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of options (in shares)	138,617	138,617
Issuance of common stock upon exercise of options	$ 47			47
Issuance of common stock upon release of restricted stock units (in shares)		873,070
Cancellation of shares used to settle payroll tax withholding (in shares)		(244,202)
Cancellation of shares used to settle payroll tax withholding	(2,808)			(2,808)
Issuance of common stock upon exercise of warrants (in shares)		20
Stock-based compensation expense	2,760			2,760
Net loss	(5,709)				(5,709)
Balance at end of period (in shares) at Mar. 31, 2022		152,606,563
Balance at end of period at Mar. 31, 2022	$ 199,449	$ 16	$ 0	$ 745,752	$ (546,319)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Cash flows from operating activities:
Net loss	$ (5,709)	$ (154,918)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	196	130
Non-cash interest expense	14	21
Non-cash lease expense	275	0
Stock-based compensation expense	2,760	129
Change in fair value of warrant liabilities	(15,664)	8,426
Loss on revaluation of derivative liabilities	0	138,141
Change in earnout liabilities	(840)	0
Changes in operating assets and liabilities:
Accounts receivable	785	0
Prepaid expenses and other assets	405	(294)
Prepaid expenses and other assets	(1,596)	1,882
Net cash used in operating activities	(19,374)	(6,483)
Cash flows from investing activities:
Purchases of property and equipment	(4,041)	(133)
Net cash used in investing activities	(4,041)	(133)
Cash flows from financing activities:
Principal payments on notes payable	(483)	(101)
Proceeds from stock options exercised	47	518
Repurchase of shares from employees for income tax withholding purposes	(2,808)	0
Proceeds from sale of Legacy ESS Series C-2 redeemable convertible preferred stock, net of issuance costs	0	11,461
Net cash (used in) provided by financing activities	(3,244)	11,878
Net change in cash, cash equivalents and restricted cash	(26,659)	5,262
Cash, cash equivalents and restricted cash, beginning of period	240,232	6,394
Cash, cash equivalents and restricted cash, end of period	213,573	11,656
Supplemental disclosures of cash flow information:
Cash paid for operating leases included in cash used in operating activities	403	0
Non-cash investing and financing transactions:
Purchase of property and equipment included in accounts payable and accrued and other current liabilities	2,235	22
Right-of-use operating lease assets obtained in exchange for lease obligations	4,534	0
Right-of-use finance lease assets obtained in exchange for lease obligations	123	0
Extinguishment of derivative liabilities upon sale of Legacy ESS Series C-2 redeemable convertible preferred stock, net of amount allocated to warrants	0	18,055
Extinguishment of warrant liabilities upon exercise of Legacy ESS Series B, Series C-1 and Series C-2 redeemable convertible preferred stock warrants	0	356
Cash and cash equivalents	212,331	10,163
Restricted cash, current	1,167	1,167
Restricted cash, non-current	75	326
Total cash, cash equivalents and restricted cash shown in the statements of cash flows	$ 213,573	$ 11,656

DESCRITPION OF BUSINESS AND BAS

DESCRITPION OF BUSINESS AND BASIS OF PRESENTATION	3 Months Ended
	Mar. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
DESCRITPION OF BUSINESS AND BASIS OF PRESENTATION	DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION Description of Business —ESS Tech, Inc. (“ESS” or the “Company”) is a long-duration energy storage company specializing in iron flow battery technology. ESS develops long-duration iron flow batteries for commercial and utility-scale energy storage applications requiring four or more hours of flexible energy capacity. The Company’s products are designed for a 25-year operating life without performance degradation, and with minimal annual operational and maintenance requirements. The Company is in the research and development phase. Its products are still being developed and do not yet meet standard specifications to be sold commercially (“Commercially Available”). The Company was originally incorporated as a Cayman Islands exempted company on July 21, 2020 as a publicly traded special purpose acquisition company under the name ACON S2 Acquisition Corp. (“STWO”) for the purpose of effecting a merger, share exchange, asset acquisition, share purchase, reorganization or similar business combination involving STWO and one or more businesses. On October 8, 2021 (the “Closing Date”), the Company consummated the merger agreement (the “Merger Agreement”) dated May 6, 2021, by and among STWO, SCharge Merger Sub, Inc., a Delaware corporation and wholly owned direct subsidiary of STWO (“Merger Sub”), and ESS Tech, Inc., a Delaware corporation (“Legacy ESS”) following the approval at a special meeting of the stockholders of STWO held on October 5, 2021. Pursuant to the terms of the Merger Agreement, STWO deregistered by way of continuation under the Cayman Islands Companies Act (2021 Revision) and registered as a corporation in the State of Delaware under Part XII of the Delaware General Corporation Law (the “Domestication”), and a business combination between STWO and Legacy ESS was effected through the merger of Merger Sub with and into Legacy ESS, with Legacy ESS surviving as a wholly owned subsidiary of STWO (together with the other transactions described in the Merger Agreement, the “Business Combination”). On the Closing Date, STWO changed its name from “ACON S2 Acquisition Corp” to “ESS Tech, Inc.”, and its common shares of stock and warrants for shares of ESS common stock commenced trading on the New York Stock Exchange under the new ticker symbols “GWH” and “GWH.W”, respectively. Basis of Presentation —The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiary and have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). Pursuant to the Merger Agreement, the merger between Merger Sub and Legacy ESS was accounted for as a reverse recapitalization in accordance with U.S. GAAP (the “Reverse Recapitalization”). Under this method of accounting, STWO was treated as the “acquired” company and Legacy ESS was treated as the acquirer for financial reporting purposes. Accordingly, for accounting purposes, the Reverse Recapitalization was treated as the equivalent of Legacy ESS issuing stock for the net assets of STWO, accompanied by a recapitalization. The net assets of STWO were stated at historical cost, with no goodwill or other intangible assets recorded. Legacy ESS was determined to be the accounting acquirer based on the following predominant factors: • Legacy ESS’s existing stockholders had the greatest voting interest in the Company; • Legacy ESS’s directors represented all of the new board of directors of the Company; • Legacy ESS’s senior management continued as the senior management of the Company; and, • Legacy ESS had the larger employee base. The assets, liabilities and results of operations prior to the Reverse Recapitalization are those of Legacy ESS. The shares and corresponding capital amounts and losses per share, prior to the Reverse Recapitalization, have been retroactively restated based on shares reflecting the exchange ratio of approximately 1.47 (the “Per Share Consideration”) established in the Business Combination. Unaudited Interim Financial Statements —The accompanying unaudited consolidated financial statements have been prepared in accordance with U.S. GAAP for interim financial information and in accordance with the rules and regulations of the SEC. Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. The unaudited consolidated financial statements reflect all normal and recurring adjustments that are, in the opinion of the Company’s management, necessary in order to make the consolidated financial statements not misleading. Operating results for the three months ended March 31, 2022 are not necessarily indicative of the results that may be expected for the year ending December 31, 2022. These unaudited interim consolidated financial statements should be read in conjunction with the consolidated financial statements and related notes included in our Annual Report on Form 10-K for the fiscal year ended December 31, 2021, as filed with the SEC on March 4, 2022. Reclassifications —Certain prior year amounts have been reclassified to conform with current year presentation.

SIGNIFICANT ACCOUNTING POLICIES

SIGNIFICANT ACCOUNTING POLICIES	3 Months Ended
	Mar. 31, 2022
Accounting Policies [Abstract]
SIGNIFICANT ACCOUNTING POLICIES	SIGNIFICANT ACCOUNTING POLICIES Use of Estimates —The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates, judgments and assumptions that affect the reported amounts of assets and liabilities and disclosure of commitments and contingencies as of the date of the consolidated financial statements and the reported amounts of expenses during the reporting periods. Such estimates relate to, among others, the useful lives and assessment of recoverability of property and equipment, deferred tax assets valuation, determination of the fair value of the Company’s earnout warrant liabilities and private warrants, as well as other accruals. These estimates are based on historical trends, market pricing, current events and other relevant assumptions and data points. Actual results could differ from those estimates and such differences may be material to the consolidated financial statements. Net Loss Per Share —The Company follows the two-class method when computing net income (loss) per common share when shares are issued that meet the definition of participating securities. Under this method, net earnings are reduced by the amount of dividends declared in the current period for common shareholders and participating security holders. The remaining earnings or “undistributed earnings” are allocated between common stock and participating securities to the extent that each security may share in earnings as if all the earnings for the period had been distributed. Once calculated, the earnings per common share is computed by dividing the net income (loss) attributable to common shareholders by the weighted average number of common shares outstanding during each year presented. Diluted income (loss) attributable to common shareholders per common share has been computed by dividing the net income (loss) attributable to common shareholders by the weighted average number of common shares outstanding plus the dilutive effect of outstanding options, warrants, and restricted stock units (“RSU”) during the respective periods computed using the treasury method. In cases where the Company has a net loss, no dilutive effect is shown as options, warrants, RSU, and earnout shares pending satisfaction of a regulatory holding period become anti-dilutive. Cash and Cash Equivalents —The Company considers all highly liquid investments with an original maturity of three months or less when purchased to be cash equivalents. Cash equivalents are recorded at carrying value, which approximates fair value. Cash and cash equivalents include cash in bank accounts and money market funds. Restricted Cash — Restricted cash is required as collateral for certain of the Company’s lease agreements and contractual supply and service arrangements. Restricted cash includes a certificate of deposit for the Company’s lease agreements and a performance and payment bond for the Company’s supply and service arrangements. The certificate of deposit and bond are recorded at carrying value, which approximates fair value. Restricted cash amounts are reported in the consolidated balance sheets as current or non-current depending on when the cash will be contractually released. Revenue Recognition —The Company did not recognize any revenue in either of the three month periods ended March 31, 2022 or 2021. The Company will recognize revenue in accordance with the requirements of, and the guidance provided by Accounting Standards Codification (“ASC”) 606, Revenue from Contracts with Customers (Topic 606) . Stock-Based Compensation —The Company accounts for stock-based compensation in accordance with ASC 718, Compensation – Stock Compensation . The Company measures and recognizes compensation expense for all stock-based awards based on estimated fair values on the date of the grant, recognized over the requisite service period. For awards that vest solely based on a service condition, the Company recognizes stock-based compensation expense on a straight-line basis over the requisite service period. The compensation expense related to awards with performance conditions is recognized over the requisite service period when the performance conditions are probable of being achieved. The compensation expense related to awards with market conditions is recognized on an accelerated attribution basis over the requisite service period identified as the derived service period over which the market conditions are expected to be achieved, and is not reversed if the market condition is not satisfied. The Company accounts for forfeitures as they occur. Stock-based awards granted to employees are primarily stock options and RSUs. The fair value of each stock option granted is estimated using the Black-Scholes Merton option-pricing model using the single-option award approach. The following assumptions are used in the Black-Scholes Merton option-pricing model: Risk-Free Interest Rate —The risk-free interest rate is based on the implied yield available on the date of grant on U.S. Treasury zero-coupon issued with a term that is equal to the option’s expected term at the grant date. Expected Volatility —The Company estimates the volatility for option grants by evaluating the average historical volatility of a peer group of companies for the period immediately preceding the option grant for a term that is approximately equal to the option’s expected term. Expected Term —The expected term for employees represents the period over which options granted are expected to be outstanding using the simplified method, as the Company’s historical share option exercise experience does not provide a reasonable basis upon which to estimate the expected term. The simplified method deems the term to be the average of the time-to-vesting and contractual life of the stock-based awards. Dividend Yield —The Company has not declared or paid dividends to date and does not anticipate declaring dividends. As such, the dividend yield has been estimated to be zero. Fair Value —The Company follows ASC 820, Fair Value Measurements (“ASC 820”) , which establishes a common definition of fair value to be applied when U.S. GAAP requires the use of fair value, establishes a framework for measuring fair value, and requires certain disclosure about such fair value measurements. ASC 820 establishes a hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that observable inputs be used when available. Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about what market participants would use in pricing the asset or liability based on the best information available in the circumstances. The hierarchy is broken down into three levels based on the reliability of inputs as follows: Level 1: Observable inputs such as quoted prices in active markets for identical assets or liabilities to which the Company has access at a measurement date. Level 2: Observable inputs other than Level 1 quoted prices that are observable for the asset or liability, either directly or indirectly; these include quoted prices for similar assets or liabilities in an active market, quoted prices for identical assets and liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3: Unobservable inputs for which little or no market data exists and for which the Company must develop its own assumptions regarding the assumptions that market participants would use in pricing the asset or liability, including assumptions regarding risk. Because of the uncertainties inherent in the valuation of assets or liabilities for which there are no observable inputs, those estimated fair values may differ significantly from the values that may have been used had a ready market for the assets or liabilities existed. Recent Accounting Pronouncements —Pursuant to the Jumpstart Our Business Startups Act (“JOBS Act”), an emerging growth company is provided the option to adopt new or revised accounting standards that may be issued by the FASB or the SEC either (i) within the same periods as those otherwise applicable to non-emerging growth companies or (ii) within the same time periods as private companies. The Company has elected to use the extended transition period for complying with any new or revised financial accounting standards. As a result, the Company’s consolidated financial statements may not be comparable to the financial statements of issuers who are required to comply with the effective date for new or revised accounting standards that are applicable to public companies. The Company also intends to continue to take advantage of some of the reduced regulatory and reporting requirements of emerging growth companies pursuant to the JOBS Act so long as the Company qualifies as an emerging growth company. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”), which requires the measurement and recognition of expected credit losses for financial assets held at amortized cost. ASU 2016-13 replaces the existing incurred loss impairment model with a forward-looking expected credit loss model, which will result in earlier recognition of credit losses. ASU 2016-13 is effective for emerging growth companies for fiscal years beginning after December 15, 2022, and interim periods within those fiscal years. The Company is currently evaluating the impact that the standard will have on its consolidated financial statements and related disclosures. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”), which simplifies the accounting for income taxes. ASU 2019-12 is effective for emerging growth companies for fiscal years beginning after December 15, 2021, and interim periods within fiscal years beginning after December 15, 2022. The Company is currently evaluating the impact that the standard will have on its consolidated financial statements and related disclosures. Recently Adopted Accounting Pronouncements —On January 1, 2022, the Company adopted ASU 2016-02, Leases (ASC 842), which superseded previous guidance related to accounting for leases within Topic 840, Leases . The Company elected the practical expedient provided under ASU 2018-11, Leases (Topic 842) Targeted Improvements , which amended ASU 2016-02 to provide entities an optional transition practical expedient to adopt the new standard with a cumulative effect adjustment as of the beginning of the year of adoption with prior year comparative financial information and disclosures remaining as previously reported. As a result, no adjustments were made to the consolidated balance sheet prior to January 1, 2022 and amounts are reported in accordance with historical accounting under Topic 840, while the consolidated balance sheet as of March 31, 2022 is presented under Topic 842. The Company elected the package of practical expedients permitted under the transition guidance, which allowed it to carry forward historical lease classification, assessment on whether a contract was or contains a lease, and assessment of initial direct costs for any leases that existed prior to January 1, 2022. The Company also elected to combine its lease and non-lease components and to keep leases with an initial term of 12 months or less off the consolidated balance sheet and recognize the associated lease payments in the consolidated statements of operations on a straight-line basis over the lease term. For new required disclosures and further information see Note 8, Leases. Adoption of the new standard resulted in the recording of lease assets and lease liabilities of $4,534 thousand and $5,229 thousand, respectively, as of January 1, 2022. The transition did not have a material impact on the Company’s results of operations, cash flows or liquidity measures.

BUSINESS COMBINATION

BUSINESS COMBINATION	3 Months Ended
	Mar. 31, 2022
Business Combination and Asset Acquisition [Abstract]
BUSINESS COMBINATION	BUSINESS COMBINATION As discussed in Note 1, on October 8, 2021, the Company consummated the Business Combination pursuant to the Merger Agreement, with Legacy ESS surviving the Business Combination as a wholly owned subsidiary of the Company. Upon the Business Combination closing (the “Closing”), each share of Legacy ESS’s common stock, par value $0.0001 per share (“Legacy ESS Common Stock”) and Preferred Stock, par value $0.0001 per share (“Legacy ESS Preferred Stock”), were converted into the right to receive shares of the Company’s common stock at the Per Share Consideration as calculated pursuant to the Merger Agreement. The aggregate consideration paid to Legacy ESS stockholders in connection with the Business Combination (excluding any potential Earnout Shares (see below for definition)), was 99,700,326 shares of the Company’s common stock (including 125,958 shares of common stock issued following the Closing as a result of a transaction expense adjustment as disclosed in the Company’s Form 8-K filed with the SEC on November 15, 2021). Pursuant to the Merger Agreement, the Company was permitted to issue to eligible Legacy ESS securityholders, on a pro rata basis, up to 16,500,000 shares of additional common stock (the “Earnout Shares”) less any RSUs issued pursuant to the Incentive RSU Pool, issuable in two equal tranches upon the occurrence of the respective Earnout Milestone Events. The Earnout Milestone Events were achieved on November 9, 2021 and Legacy ESS issued 15,674,965 shares to securityholders.

NET LOSS PER SHARE

NET LOSS PER SHARE	3 Months Ended
	Mar. 31, 2022
Earnings Per Share [Abstract]
NET LOSS PER SHARE	LOSS PER SHARE The following table presents the calculation of basic and diluted net loss per share attributable to common stockholders (in thousands, except per share data): Three Months Ended 2022 2021 Net loss attributable to common stockholders $ (5,709) $ (154,918) Weighted-average shares outstanding – Basic and Diluted 151,683,819 61,693,067 Net loss per share – Basic and Diluted $ (0.04) $ (2.51) Due to the net losses for the three months ended March 31, 2022 and 2021, basic and diluted net loss per common share were the same, as the effect of potentially dilutive securities would have been anti-dilutive. The following outstanding balances of common share equivalent securities have been excluded from the calculation of diluted weighted-average common shares outstanding because the effect is anti-dilutive for the periods presented: March 31, 2022 March 31, 2021 Stock options 3,707,113 4,379,633 RSUs 4,633,968 — Warrants 11,461,227 3,362,047 Number of securities outstanding 19,802,308 7,741,680

PREPAID EXPENSES AND OTHER CURR

PREPAID EXPENSES AND OTHER CURRENT ASSETS	3 Months Ended
	Mar. 31, 2022
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
PREPAID EXPENSES AND OTHER CURRENT ASSETS	PREPAID EXPENSES AND OTHER CURRENT ASSETS Prepaid expenses and other current assets consist of the following (in thousands): March 31, 2022 December 31, 2021 Insurance $ 2,397 $ 3,482 Vendor advances 1,514 1,103 Other 495 259 Total prepaid expenses and other current assets $ 4,406 $ 4,844

PROPERTY AND EQUIPMENT, NET

PROPERTY AND EQUIPMENT, NET	3 Months Ended
	Mar. 31, 2022
Property, Plant and Equipment [Abstract]
PROPERTY AND EQUIPMENT, NET	PROPERTY AND EQUIPMENT, NET Property and equipment, net consist of the following (in thousands): March 31, 2022 December 31, 2021 Machinery and equipment $ 2,910 $ 2,868 Furniture and fixtures 88 90 Leasehold improvements 1,030 746 Construction in process 7,944 2,517 Total property and equipment 11,972 6,221 Less accumulated depreciation (1,916) (1,720) Total property and equipment, net $ 10,056 $ 4,501

ACCRUED AND OTHER CURRENT LIABI

ACCRUED AND OTHER CURRENT LIABILITIES	3 Months Ended
	Mar. 31, 2022
Payables and Accruals [Abstract]
ACCRUED AND OTHER CURRENT LIABILITIES	ACCRUED AND OTHER CURRENT LIABILITIES Accrued and other current liabilities consist of the following (in thousands): March 31, 2022 December 31, 2021 Payroll and related benefits $ 1,552 $ 1,876 Materials and related purchases 2,596 2,108 Deferred rent — 142 Professional and consulting fees 1,140 1,820 Other 1,327 541 Total accrued and other current liabilities $ 6,615 $ 6,487

LEASES

LEASES	3 Months Ended
	Mar. 31, 2022
Leases [Abstract]
LEASES	LEASES The Company determines if an arrangement is a lease at inception and whether the arrangement is classified as an operating or finance lease. At commencement of the lease, the Company records a right-of-use (“ROU”) asset and lease liability in the consolidated balance sheets based on the present value of lease payments over the term of the arrangement. ROU assets represent the right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. As the Company’s leases do not provide an implicit rate, it uses its incremental borrowing rate based on the information available at commencement date in determining the present value of lease payments. The Company determines its incremental borrowing rate based on publicly available data for instruments with similar characteristics, including recently issued debt, as well as other factors. Contract terms may include options to extend or terminate the lease, and when the Company deems it reasonably certain that ESS will exercise that option it is included in the ROU asset and lease liability. Operating leases will reflect lease expense on a straight-line basis, while finance leases will result in the separate presentation of interest expense on the lease liability and amortization expense of the ROU asset. ROU assets related to the Company’s operating leases are included in operating lease ROU assets, while the corresponding lease liabilities are included in current and non-current operating lease liabilities on our consolidated balance sheets. ROU assets related to the Company’s finance leases are included in other non-current assets, while the corresponding lease liabilities are included in accrued and other current liabilities and other non-current liabilities on the Company’s consolidated balance sheets. The Company does not record leases with a term of 12-months or less in the consolidated balance sheets. There was no short-term lease cost for the three months ended March 31, 2022. The Company leases office and manufacturing space in Wilsonville, Oregon under operating leases and printers and copiers under finance leases. Each of the operating leases provides the Company an option to renew the lease for an additional 60 months which have not been included in the operating lease obligations. Operating lease costs for the three months ended March 31, 2022 were $371 thousand. As of March 31, 2022, the weighted-average remaining term for the operating leases was 3.4 years and the weighted-average discount rate was 7.5%. The weighted-average remaining term for the finance lease was 4.9 years and the weighted-average discount rate was 7.5%. As of March 31, 2022 future maturities of lease liabilities are as follows (in thousands): Operating Leases Finance Leases 2022 $ 1,222 $ 21 2023 1,670 30 2024 1,720 30 2025 983 30 2026 — 30 Thereafter — 7 Total minimum lease payments $ 5,595 $ 148 Less imputed interest (673) (25) Total $ 4,922 $ 123
LEASES	LEASES The Company determines if an arrangement is a lease at inception and whether the arrangement is classified as an operating or finance lease. At commencement of the lease, the Company records a right-of-use (“ROU”) asset and lease liability in the consolidated balance sheets based on the present value of lease payments over the term of the arrangement. ROU assets represent the right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. As the Company’s leases do not provide an implicit rate, it uses its incremental borrowing rate based on the information available at commencement date in determining the present value of lease payments. The Company determines its incremental borrowing rate based on publicly available data for instruments with similar characteristics, including recently issued debt, as well as other factors. Contract terms may include options to extend or terminate the lease, and when the Company deems it reasonably certain that ESS will exercise that option it is included in the ROU asset and lease liability. Operating leases will reflect lease expense on a straight-line basis, while finance leases will result in the separate presentation of interest expense on the lease liability and amortization expense of the ROU asset. ROU assets related to the Company’s operating leases are included in operating lease ROU assets, while the corresponding lease liabilities are included in current and non-current operating lease liabilities on our consolidated balance sheets. ROU assets related to the Company’s finance leases are included in other non-current assets, while the corresponding lease liabilities are included in accrued and other current liabilities and other non-current liabilities on the Company’s consolidated balance sheets. The Company does not record leases with a term of 12-months or less in the consolidated balance sheets. There was no short-term lease cost for the three months ended March 31, 2022. The Company leases office and manufacturing space in Wilsonville, Oregon under operating leases and printers and copiers under finance leases. Each of the operating leases provides the Company an option to renew the lease for an additional 60 months which have not been included in the operating lease obligations. Operating lease costs for the three months ended March 31, 2022 were $371 thousand. As of March 31, 2022, the weighted-average remaining term for the operating leases was 3.4 years and the weighted-average discount rate was 7.5%. The weighted-average remaining term for the finance lease was 4.9 years and the weighted-average discount rate was 7.5%. As of March 31, 2022 future maturities of lease liabilities are as follows (in thousands): Operating Leases Finance Leases 2022 $ 1,222 $ 21 2023 1,670 30 2024 1,720 30 2025 983 30 2026 — 30 Thereafter — 7 Total minimum lease payments $ 5,595 $ 148 Less imputed interest (673) (25) Total $ 4,922 $ 123

BORROWINGS

BORROWINGS	3 Months Ended
	Mar. 31, 2022
Debt Disclosure [Abstract]
BORROWINGS	BORROWINGS Long term debt consists of the following (in thousands): March 31, 2022 December 31, 2021 Total notes payable $ 3,300 $ 3,769 Less current portion of notes payable 1,817 1,900 Notes payable, non-current $ 1,483 $ 1,869 Notes Payable In 2018, the Company entered into a $1,000 thousand note payable with a bank that was secured by all property of the Company, except for its intellectual property. The note payable’s original maturity date was July 1, 2021. In March 2020, the Company amended the note payable and borrowed an additional $4,000 thousand. The additional $4,000 thousand borrowing changed the present value of cash flows by more than 10% and, as such, was treated as a debt extinguishment. The Company recognized a $62 thousand loss on extinguishment of debt for the year ended December 31, 2021. The Company’s notes payable to the bank were recorded at fair value as part of the extinguishment. The $4,000 thousand note payable’s original maturity date was January 1, 2023. In April 2020, the Company entered into a deferral agreement (“Deferral Agreement”) to extend the maturity date of the original $1,000 thousand note payable to September 1, 2022 and extend the maturity date of the additional $4,000 thousand note payable to January 1, 2024. The Company accounted for the Deferral Agreement as a debt modification based on an analysis of cash flows before and after the debt modification.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	3 Months Ended
	Mar. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES The Company, from time to time, is a party to various claims, legal actions, and complaints arising in the ordinary course of business. The Company is not aware of any legal proceedings or other claims, legal actions, or complaints through the date of issuance of these consolidated financial statements. As of March 31, 2022, and December 31, 2021, the Company had a standby letter of credit with First Republic Bank totaling $725 thousand as security for an operating lease of office and manufacturing space in Wilsonville, Oregon. As of March 31, 2022 the letter of credit was secured by a restricted certificate of deposit account totaling $75 thousand. There were no draws against the letter of credit during the three months ended March 31, 2022 and 2021. The Company purchases materials from several suppliers and has entered into agreements with various contract manufacturers, which include cancellable and noncancellable purchase commitments. As of March 31, 2022 and December 31, 2021, total unfulfilled noncancellable purchase commitments were $23,344 thousand and $10,160 thousand, respectively. In addition, total unfulfilled cancellable purchase commitments amounted to $3,539 thousand and $10,446 thousand as of March 31, 2022, and December 31, 2021, respectively. These purchase commitments were not recorded in the consolidated financial statements.

LEGACY ESS REDEEMABLE CONVERTIB

LEGACY ESS REDEEMABLE CONVERTIBLE PREFERRED STOCK	3 Months Ended
	Mar. 31, 2022
Temporary Equity Disclosure [Abstract]
LEGACY ESS REDEEMABLE CONVERTIBLE PREFERRED STOCK	LEGACY ESS REDEEMABLE CONVERTIBLE PREFERRED STOCK All Legacy ESS redeemable convertible preferred stock classified as redeemable was converted into Legacy ESS common stock, which was subsequently exchanged for the Company’s common stock as a result of the Business Combination using the Per Share Consideration of approximately 1.47. All preferred stock amounts have been retroactively adjusted to reflect the Business Combination. Immediately prior to the completion of the Business Combination on October 8, 2021, all outstanding shares of Legacy ESS’s redeemable convertible preferred stock converted into an aggregate 57,104,332 shares of common stock. Legacy ESS Rights to Purchase Series C-2 Convertible Preferred Stock Legacy ESS’s Series C redeemable convertible preferred stock financing agreement initially provided additional committed funding of up to $79,999 thousand, through the purchase of up to 39,971,716 shares of Series C-2 redeemable convertible preferred stock based on the completion of certain operational milestones at a predetermined price of $2.00 per share, to certain Series C-1 Investors. Legacy ESS determined that its obligation to issue, and Legacy ESS’s investors’ obligation to purchase shares of Series C-2 redeemable convertible preferred stock at a fixed price represents a freestanding derivative financial instrument (the “Series C-2 Redeemable Convertible Preferred Stock Issuance Right”). The Series C-2 Redeemable Convertible Preferred Stock Issuance Right was initially recorded at fair value and was adjusted to fair value at each reporting date, with the change in fair value recorded as a revaluation of derivative liabilities as a component of other income and expense in the consolidated statement of operations. The Series C-2 Redeemable Convertible Preferred Stock Issuance Right was initially scheduled to expire in August 2021 and was classified as a non-current derivative liability as of March 31, 2021. The Series C-2 Redeemable Convertible Preferred Stock Issuance Right was initially valued at a fair value of $11,379 thousand. Sale of Legacy ESS Series C-2 Redeemable Convertible Preferred Stock In March 2021, Legacy ESS issued 5,746,003 shares of Series C-2 redeemable convertible preferred stock for $2.00 per share, totaling $11,500 thousand. Legacy ESS incurred $39 thousand in costs associated with the issuance. In connection with the sale of the Series C-2 redeemable convertible preferred stock, Legacy ESS issued warrants to purchase 861,896 shares of Series C-2 redeemable convertible preferred stock and extinguished a portion of the C-2 Purchase Right for 5,746,003 shares. The warrants were exercisable at a price of $0.0001 per share. The extinguishment of a portion of the Series C-2 Redeemable Convertible Preferred Stock Issuance Right reduced Legacy ESS’s derivative liabilities and increased the amount attributable to the issuance by $23,152 thousand. Total transaction value of $34,613 thousand was allocated to the Series C-2 redeemable convertible preferred stock and warrants in the amounts of $29,516 thousand and $5,096 thousand, respectively. Amendment to Legacy ESS Series C-2 Redeemable Convertible Preferred Stock Purchase Right and Related Warrants On May 7, 2021, Legacy ESS amended its Series C-2 Preferred Stock Purchase Agreement and Amendment to Series C Preferred Stock Purchase Agreement. Under the terms of the amended agreement, the number of shares of C-2 Convertible Redeemable Preferred Stock required to be issued by Legacy ESS and purchased by investors under the C-2 Redeemable Convertible Preferred Stock Purchase Right were adjusted, and Legacy ESS issued Series C-2 warrants. The Series C-2 warrants were exercisable at a price of $.00007 per share upon a successful Business Combination with STWO. The investors were permitted to purchase shares subject to the C-2 Redeemable Convertible Preferred Stock Purchase Right at any time and must purchase the shares upon the Company’s achievement of specific milestones. The number of shares subject to and potential proceeds from the C-2 Redeemable Convertible Preferred Stock Purchase Agreement and related C-2 Warrants were as follows: As of May 7, 2021 Upon completion of the Business Combination Quantity Price Series C-2 Redeemable Convertible Preferred Stock Purchase Right 7,994,442 $ 2.00 Series C-2 Warrant exercisable upon completion of the Business Combination 21,159,364 $ 0.00007 The C-2 warrants and Purchase Rights were exercised in conjunction with the Business Combination which cl osed on October 8, 2021 and the Company received proceeds of $15,559 thousand, which were net of $439 thousand in issuance costs . The Company recorded a net increase in the derivative liability of $138,141 thousand for the three months ended March 31, 2021 for changes in the estimated fair value of the Series C-2 Redeemable Convertible Preferred Stock Purchase Right and C-2 Warrant exercisable upon completion of the Business Combination. Legacy ESS Warrants Legacy ESS Series B redeemable convertible preferred stock warrants were issued at exercise prices ranging from $0.0007 per share to $0.83 per share. 100,161 shares of Series B redeemable convertible preferred stock warrants had a 10-year exercise period and the remainder did not expire until a significant transaction had occurred, as defined by the warrant purchase agreement. The warrants were fully vested at the issuance date. Legacy ESS Series C-1 and C-2 redeemable convertible preferred stock warrants were issued with prices ranging from $0.00007 to $1.25 per share, a life of 10 years and were fully vested at issuance. Legacy ESS common stock warrants, all issued at a price of $0.0007 per share, were recorded at fair value within equity. Legacy ESS common stock warrants were fully vested at issuance and did not expire until a significant transaction has occurred, as defined by the Warrant Purchase Agreement. In connection with the Business Combination, all Legacy ESS warrants were exercised during the year ended December 31, 2021.

COMMON STOCK WARRANTS

COMMON STOCK WARRANTS	3 Months Ended
	Mar. 31, 2022
Equity [Abstract]
COMMON STOCK WARRANTS	COMMON STOCK WARRANTSAs of March 31, 2022, the Company had 7,377,893 warrants to purchase common stock listed on the New York Stock Exchange (“NYSE”) under the ticker symbol “GWH.W” (the “Public Warrants”), 3,500,000 warrants to purchase common stock issued in a private placement concurrently with STWO’s initial public offering (the “Private Warrants”) and 583,334 Earnout Warrants (as defined below) outstanding. As part of STWO’s initial public offering, 8,333,287 Public Warrants were sold. The Public Warrants entitle the holder thereof to purchase one share of common stock at a price of $11.50 per share, subject to adjustments. The Public Warrants may be exercised only for a whole number of shares of common stock. No fractional shares will be issued upon exercise of the warrants. The Public Warrants will expire five years after completion of the business combination, on October 8, 2026, or earlier upon redemption or liquidation. The Company may call the Public Warrants for redemption starting anytime, in whole and not in part, at a price of $0.01 per warrant, so long as the Company provides not less than 30 days prior written notice of redemption to each warrant holder, and if, and only if, the reported last sale price of common stock equals or exceeds $18.00 per share or $10.00 per share for any 20 trading days within a 30-trading day period ending on the third trading day prior to the date the Company sends the notice of redemption to the warrant holders provided there is an effective registration statement covering the shares of common stock issuable upon exercise of the warrants. The Company may call the Public Warrants for redemption starting anytime, in whole and not in part, at a price of $0.10 per warrant, so long as the Company provides not less than 30 days prior written notice of redemption to each warrant holder; provided that holders will be able to exercise their warrants on a cashless basis prior to redemption and receive a number of shares determined based on the redemption date fair market value of the shares, and if, and only if, the reported last sale price of common stock equals or exceeds $10.00 per share or $10.00 per share for any 20 trading days within a 30-trading day period ending on the third trading day prior to the date the Company sends the notice of redemption to the warrant holders provided there is an effective registration statement covering the shares of common stock issuable upon exercise of the warrants. Simultaneously with STWO’s initial public offering, STWO consummated a private placement of 4,666,667 Private Warrants with STWO’s sponsor. In connection with the Business Combination, STWO’s sponsor agreed to forfeit 583,333 Private Warrants. Of the remaining 4,083,334 Private Warrants, 3,500,000 were immediately vested and 583,334 warrants (the “Earnout Warrants”) were vested upon meeting certain Earnout Milestone Events on November 9, 2021. Each Private Warrant and Earnout Warrant is exercisable for one share of common stock at a price of $11.50 per share, subject to adjustment. The Private Warrants and Earnout Warrants, post vesting on November 9, 2021, are identical to the Public Warrants, except that the Private Warrants and Earnout Warrants and the shares of common stock issuable upon exercise of the Private Warrants are not transferable, assignable or salable until 30 days after the completion of a Business Combination, subject to certain limited exceptions. Additionally, the Private Warrants and Earnout Warrants are non-redeemable so long as they are held by the initial purchasers or such purchasers’ permitted transferees. If the Private Warrants and Earnout Warrants are held by someone other than their initial purchasers or their permitted transferees, then the Private Warrants and Earnout Warrants will be redeemable by the Company and exercisable by such holders on the same basis as the Public Warrants. Additionally, if the Company redeems the Public Warrants when the common stock equals or exceeds $10.00 per share for any 20 trading days within a 30-day period ending on the third trading day prior to the date the Company sends the notice of redemption to warrant holders and the closing price of the common share for any 20 trading days within the same period is less than $18.00 per share, the Company must concurrently redeem the Private Warrants and Earnout Warrants. The table below shows the common stock warrant activities during the three months ended March 31, 2022: December 31, 2021 Issued Exercised March 31, 2022 Earnout Warrants 583,334 — — 583,334 Public Warrants 7,377,913 — 20 7,377,893 Private Warrants 3,500,000 — — 3,500,000 Total Common Stock Warrants 11,461,247 — 20 11,461,227 The Company’s common stock warrants were initially recorded at fair value upon completion of the Business Combination and are adjusted to fair value at each reporting date based on the market price of the Public Warrants, with the change in fair value recorded as a component of other income and expense in the consolidated statements of operations. For the three months ending March 31, 2022, the Company recorded a net decrease to the liabilities for Earnout Warrants, Public Warrants and Private Warrants of

STOCK-BASED COMPENSATION PLAN

STOCK-BASED COMPENSATION PLAN	3 Months Ended
	Mar. 31, 2022
Share-based Payment Arrangement [Abstract]
STOCK-BASED COMPENSATION PLAN	STOCK-BASED COMPENSATION PLAN 2021 Equity Incentive Plan In October 2021, the Board of Directors of the Company adopted the ESS Tech Inc. 2021 Equity Incentive Plan (the “2021 Plan”). The 2021 Plan became effective upon consummation of the Business Combination. The stock awards may be issued as Incentive Stock Options (“ISO”), Non-statutory Stock Options (“NSO”), Stock Appreciation Rights, Restricted Stock Awards, or Restricted Stock Unit Awards. Only employees are eligible to receive ISO awards. Employees, directors, and consultants who are providing continuous service to the Company are eligible to receive stock awards other than ISOs. The number of Shares available for issuance under the 2021 Plan will be increased on the first day of each fiscal year beginning with the 2022 fiscal year and ending with the 2031 Fiscal Year, in an amount equal to the lesser of (i) 15,260,000 Shares, (ii) five percent (5%) of the outstanding shares on the last day of the immediately preceding fiscal year, or (iii) such number of shares determined by the Company no later than the last day of the immediately preceding fiscal year. Under the 2021 Plan, the Company is authorized to issue 17,610,000 shares of common stock as of March 31, 2022. Option prices for incentive stock options are set at the fair market value of the Company’s common stock at the date of grant. Employee new hire options generally cliff vest at the end of the first year and then 1/48 th of the original grant over the remaining three years. Grants expire 10 years from the date of grant. No ISOs, NSOs, Restricted Stock Awards, nor Stock Appreciation Rights were outstanding as of March 31, 2022. Shares Available for Future Grant As of March 31, 2022, there were 13,021,489 shares available for future grant under the 2021 Plan. Stock option and RSU activity, prices, and values during the three months ended March 31, 2022 is as follows (in thousands, except for share, per share, and contractual term data): Options Outstanding RSUs Number of Weighted Weighted Aggregate Number of plan shares outstanding Weighted average Balances as of December 31, 2021 3,796,530 $ 0.83 8.08 $ 40,274 3,392,153 $ 10.69 Options and RSUs granted 65,717 8.00 2,150,859 5.46 Options exercised and RSUs released (138,617) 0.30 (873,070) 11.12 Options and RSUs forfeited (16,517) 0.36 (35,974) 10.15 Balances as of March 31, 2022 3,707,113 $ 0.98 8.03 $ 17,012 4,633,968 $ 8.82 Options vested and exercisable - December 31, 2021 1,827,374 $ 0.31 7.20 $ 20,337 Options vested and exercisable - March 31, 2022 1,626,013 $ 0.56 7.41 $ 8,140 In accordance with ASC 718, Compensation – Stock Compensation , the fair value of each option grant has been estimated as of the date of grant using the following weighted average assumptions: Three Months Ended March 31, 2022 2021 Risk-free rate 1.64 % 0.75 % Expected dividends — — Expected term 6 years 6 years Expected volatility 73.95 % 74.80 % Stock-based compensation expense is allocated on a departmental basis, based on the classification of the award holder. The following table presents the amount of stock-based compensation related to stock-based awards to employees on the Company’s consolidated statements of operations and comprehensive loss (in thousands): Three Months Ended March 31, 2022 2021 Research and development $ 587 $ 64 Sales and marketing 54 16 General and administrative 2,119 49 Total stock-based compensation $ 2,760 $ 129

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	3 Months Ended
	Mar. 31, 2022
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS The Company follows ASC 820, Fair Value Measurements , which establishes a common definition of fair value to be applied when U.S. GAAP requires the use of fair value, establishes a framework for measuring fair value, and requires certain disclosure about such fair value measurements. The following table presents the Company’s fair value hierarchy for its financial assets and liabilities measured at fair value on a recurring basis (in thousands): March 31, 2022 Level 1 Level 2 Level 3 Total Assets: Cash equivalents and restricted cash: Money market funds $ 211,369 $ — $ — $ 211,369 Certificate of deposit — 75 — 75 Total assets $ 211,369 $ 75 $ — $ 211,444 Liabilities: Earnout warrant liabilities $ — $ 636 $ — $ 636 Public common stock warrants 8,042 — — 8,042 Private common stock warrants — 3,815 — 3,815 Total liabilities $ 8,042 $ 4,451 $ — $ 12,493 December 31, 2021 Level 1 Level 2 Level 3 Total Assets: Cash equivalents and restricted cash: Money market funds $ 237,897 $ — $ — $ 237,897 Certificate of deposit — 125 — 125 Total assets $ 237,897 $ 125 $ — $ 238,022 Liabilities: Earnout warrant liabilities $ — $ 1,476 $ — $ 1,476 Public common stock warrants 18,666 — — 18,666 Private common stock warrants — 8,855 — 8,855 Total liabilities $ 18,666 $ 10,331 $ — $ 28,997 There were no transfers among Level 1, Level 2, or Level 3 categories during the periods presented. The carrying amounts of the Company’s notes payable, and accounts payable approximate their fair values due to their short maturities. Level 1 Assets: The Company invests in money market funds that have maturities of 90 days or less. Money market funds are classified as cash equivalents and are recorded at their carrying value, which approximates fair value. Level 2 Assets: The Company invests in a certificate of deposit with a maturity of one year from purchase date. The certificate of deposit is classified as restricted cash and is recorded at its carrying value, which approximates fair value. Level 1 Liabilities: The Company values its public common stock warrants based on the market price of the warrant. Level 2 Liabilities: The Company values its earnout warrant liabilities and private common stock warrants based on the market price of the Company’s public common stock warrants. Level 3 Liabilities: Warrants Freestanding warrants to purchase Redeemable Convertible Preferred Stock were accounted for as liability awards and recorded at fair value on their issuance date and adjusted to fair value at each reporting date, with the change in fair value being recorded as a component of other income (expenses), net. The warrants were accounted for as liabilities as the underlying shares of Preferred Stock were contingently redeemable upon occurrence of a change in control, which was outside the control of the Company. As of March 31, 2021, the Company measured its warrant liabilities using Level 3 unobservable inputs within the Black-Scholes Merton option-pricing model. The Company used various key assumptions, such as the fair value of Series B redeemable convertible preferred stock warrants and Series C redeemable convertible preferred stock warrants, the volatility of peer companies’ stock prices, the risk-free interest rate based on the U.S. Treasury yield, and the expected term (based on remaining term to a significant event for Series B redeemable convertible preferred stock warrants and remaining contractual term for Series C redeemable convertible preferred stock warrants). The Company measured the fair value of the redeemable convertible Preferred Stock warrants at each reporting date, with subsequent gains and losses from remeasurement of Level 3 financial liabilities recorded through other income (expenses), net in the consolidated statements of operations and comprehensive loss. Future Rights to Purchase Series C-2 Redeemable Convertible Preferred Stock See Note 11 for a discussion of the Company’s Series C Redeemable Convertible Preferred Stock financing agreement. The value of the Series C-2 Redeemable Convertible Preferred Stock Issuance Right was determined based on significant inputs not observable in the market, which represented a Level 3 measurement within the fair value hierarchy. The fair value of the Series C-2 Redeemable Convertible Preferred Stock Issuance Right was determined using a discounted cash flow model, which takes into account the estimated value of Series C-2 stock, estimated time to purchase, probability of purchase and the risk-free interest rate based on the U.S. Treasury yield. The Company measures the fair value of the Series C-2 Redeemable Convertible Preferred Stock Issuance Right at each reporting date, with subsequent gains and losses from remeasurement of Level 3 financial liabilities recorded through other expense, net in the consolidated statements of operations and comprehensive loss. The following table sets forth a summary of changes in the fair value of the Company’s Level 3 liabilities at fair value on a recurring basis (in thousands): Three Months Ended March 31, 2022 2021 Warrant liabilities: Beginning balance December 31 $ — $ 3,329 Change in fair value — 8,426 Fair value of warrants issued — 5,096 Fair value of warrants exercised — (356) Ending balance March 31 — 16,495 Series C-2 Convertible Preferred Stock Issuance Right liability: Beginning balance December 31 — 22,911 Change in fair value — 138,141 Fair value of derivatives extinguished — (23,152) Ending balance March 31 — 137,900 Total $ — $ 154,395

INCOME TAXES

INCOME TAXES	3 Months Ended
	Mar. 31, 2022
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXESThe Company did not record a tax provision for the three months ended March 31, 2022 and 2021, respectively, due to the Company’s history of losses, and accordingly, has recorded a valuation allowance against substantially all of the Company’s net deferred tax assets. The Company provides for a valuation allowance when it is more likely than not that some portion of, or all of the Company’s deferred tax assets will not be realized.

RELATED PARTY TRANSACTIONS

RELATED PARTY TRANSACTIONS	3 Months Ended
	Mar. 31, 2022
Related Party Transactions [Abstract]
RELATED PARTY TRANSACTIONS	RELATED PARTY TRANSACTIONS In April 2021, the Company signed a framework agreement with one of its investors, SB Energy Global Holdings One Ltd (“SBE”), to supply energy storage products to SBE in support of its market activities. Under this agreement, the Company has made various commitments to meet SBE’s potential need for energy storage products and is obligated to reserve a certain percentage of manufacturing capacity to meet SBE’s future needs, subject to periodic reviews of its firm and anticipated orders. To date, no orders have been placed under the framework agreement. Additionally, the Company entered into a preferred financing equity transaction with SBE and Breakthrough Energy Ventures, LLC as discussed in Note 11. These related parties were also issued 6,707,318 of the Earnout Shares discussed in Note 3. As of December 31, 2021, the Company had recorded accounts receivable of $66 thousand and deferred revenue of $171 thousand for sales of Energy Warehouse products to related parties.

SIGNIFICANT ACCOUNTING POLICI_2

SIGNIFICANT ACCOUNTING POLICIES (Policies)	3 Months Ended
	Mar. 31, 2022
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation —The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiary and have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). Pursuant to the Merger Agreement, the merger between Merger Sub and Legacy ESS was accounted for as a reverse recapitalization in accordance with U.S. GAAP (the “Reverse Recapitalization”). Under this method of accounting, STWO was treated as the “acquired” company and Legacy ESS was treated as the acquirer for financial reporting purposes. Accordingly, for accounting purposes, the Reverse Recapitalization was treated as the equivalent of Legacy ESS issuing stock for the net assets of STWO, accompanied by a recapitalization. The net assets of STWO were stated at historical cost, with no goodwill or other intangible assets recorded. Legacy ESS was determined to be the accounting acquirer based on the following predominant factors: • Legacy ESS’s existing stockholders had the greatest voting interest in the Company; • Legacy ESS’s directors represented all of the new board of directors of the Company; • Legacy ESS’s senior management continued as the senior management of the Company; and, • Legacy ESS had the larger employee base.
Reclassifications	Reclassifications —Certain prior year amounts have been reclassified to conform with current year presentation.
Use of Estimates	Use of Estimates—The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates, judgments and assumptions that affect the reported amounts of assets and liabilities and disclosure of commitments and contingencies as of the date of the consolidated financial statements and the reported amounts of expenses during the reporting periods. Such estimates relate to, among others, the useful lives and assessment of recoverability of property and equipment, deferred tax assets valuation, determination of the fair value of the Company’s earnout warrant liabilities and private warrants, as well as other accruals. These estimates are based on historical trends, market pricing, current events and other relevant assumptions and data points. Actual results could differ from those estimates and such differences may be material to the consolidated financial statements.
Net Loss per Share	Net Loss Per Share —The Company follows the two-class method when computing net income (loss) per common share when shares are issued that meet the definition of participating securities. Under this method, net earnings are reduced by the amount of dividends declared in the current period for common shareholders and participating security holders. The remaining earnings or “undistributed earnings” are allocated between common stock and participating securities to the extent that each security may share in earnings as if all the earnings for the period had been distributed. Once calculated, the earnings per common share is computed by dividing the net income (loss) attributable to common shareholders by the weighted average number of common shares outstanding during each year presented. Diluted income (loss) attributable to common shareholders per common share has been computed by dividing the net income (loss) attributable to common shareholders by the weighted average number of common shares outstanding plus the dilutive effect of outstanding options, warrants, and restricted stock units (“RSU”) during the respective periods computed using the treasury method. In cases where the Company has a net loss, no dilutive effect is shown as options, warrants, RSU, and earnout shares pending satisfaction of a regulatory holding period become anti-dilutive.
Cash, Cash Equivalents, and Restricted Cash	Cash and Cash Equivalents —The Company considers all highly liquid investments with an original maturity of three months or less when purchased to be cash equivalents. Cash equivalents are recorded at carrying value, which approximates fair value. Cash and cash equivalents include cash in bank accounts and money market funds. Restricted Cash — Restricted cash is required as collateral for certain of the Company’s lease agreements and contractual supply and service arrangements. Restricted cash includes a certificate of deposit for the Company’s lease agreements and a performance and payment bond for the Company’s supply and service arrangements. The certificate of deposit and bond are recorded at carrying value, which approximates fair value. Restricted cash amounts are reported in the consolidated balance sheets as current or non-current depending on when the cash will be contractually released.
Revenue Recognition	Revenue Recognition —The Company did not recognize any revenue in either of the three month periods ended March 31, 2022 or 2021. The Company will recognize revenue in accordance with the requirements of, and the guidance provided by Accounting Standards Codification (“ASC”) 606, Revenue from Contracts with Customers (Topic 606) .
Stock-Based Compensation	Stock-Based Compensation —The Company accounts for stock-based compensation in accordance with ASC 718, Compensation – Stock Compensation . The Company measures and recognizes compensation expense for all stock-based awards based on estimated fair values on the date of the grant, recognized over the requisite service period. For awards that vest solely based on a service condition, the Company recognizes stock-based compensation expense on a straight-line basis over the requisite service period. The compensation expense related to awards with performance conditions is recognized over the requisite service period when the performance conditions are probable of being achieved. The compensation expense related to awards with market conditions is recognized on an accelerated attribution basis over the requisite service period identified as the derived service period over which the market conditions are expected to be achieved, and is not reversed if the market condition is not satisfied. The Company accounts for forfeitures as they occur. Stock-based awards granted to employees are primarily stock options and RSUs. The fair value of each stock option granted is estimated using the Black-Scholes Merton option-pricing model using the single-option award approach. The following assumptions are used in the Black-Scholes Merton option-pricing model: Risk-Free Interest Rate —The risk-free interest rate is based on the implied yield available on the date of grant on U.S. Treasury zero-coupon issued with a term that is equal to the option’s expected term at the grant date. Expected Volatility —The Company estimates the volatility for option grants by evaluating the average historical volatility of a peer group of companies for the period immediately preceding the option grant for a term that is approximately equal to the option’s expected term. Expected Term —The expected term for employees represents the period over which options granted are expected to be outstanding using the simplified method, as the Company’s historical share option exercise experience does not provide a reasonable basis upon which to estimate the expected term. The simplified method deems the term to be the average of the time-to-vesting and contractual life of the stock-based awards.
Fair Value	Fair Value —The Company follows ASC 820, Fair Value Measurements (“ASC 820”) , which establishes a common definition of fair value to be applied when U.S. GAAP requires the use of fair value, establishes a framework for measuring fair value, and requires certain disclosure about such fair value measurements. ASC 820 establishes a hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that observable inputs be used when available. Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about what market participants would use in pricing the asset or liability based on the best information available in the circumstances. The hierarchy is broken down into three levels based on the reliability of inputs as follows: Level 1: Observable inputs such as quoted prices in active markets for identical assets or liabilities to which the Company has access at a measurement date. Level 2: Observable inputs other than Level 1 quoted prices that are observable for the asset or liability, either directly or indirectly; these include quoted prices for similar assets or liabilities in an active market, quoted prices for identical assets and liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3: Unobservable inputs for which little or no market data exists and for which the Company must develop its own assumptions regarding the assumptions that market participants would use in pricing the asset or liability, including assumptions regarding risk. Because of the uncertainties inherent in the valuation of assets or liabilities for which there are no observable inputs, those estimated fair values may differ significantly from the values that may have been used had a ready market for the assets or liabilities existed.
Recent Accounting Pronouncements	Recent Accounting Pronouncements —Pursuant to the Jumpstart Our Business Startups Act (“JOBS Act”), an emerging growth company is provided the option to adopt new or revised accounting standards that may be issued by the FASB or the SEC either (i) within the same periods as those otherwise applicable to non-emerging growth companies or (ii) within the same time periods as private companies. The Company has elected to use the extended transition period for complying with any new or revised financial accounting standards. As a result, the Company’s consolidated financial statements may not be comparable to the financial statements of issuers who are required to comply with the effective date for new or revised accounting standards that are applicable to public companies. The Company also intends to continue to take advantage of some of the reduced regulatory and reporting requirements of emerging growth companies pursuant to the JOBS Act so long as the Company qualifies as an emerging growth company. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”), which requires the measurement and recognition of expected credit losses for financial assets held at amortized cost. ASU 2016-13 replaces the existing incurred loss impairment model with a forward-looking expected credit loss model, which will result in earlier recognition of credit losses. ASU 2016-13 is effective for emerging growth companies for fiscal years beginning after December 15, 2022, and interim periods within those fiscal years. The Company is currently evaluating the impact that the standard will have on its consolidated financial statements and related disclosures. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”), which simplifies the accounting for income taxes. ASU 2019-12 is effective for emerging growth companies for fiscal years beginning after December 15, 2021, and interim periods within fiscal years beginning after December 15, 2022. The Company is currently evaluating the impact that the standard will have on its consolidated financial statements and related disclosures. Recently Adopted Accounting Pronouncements —On January 1, 2022, the Company adopted ASU 2016-02, Leases (ASC 842), which superseded previous guidance related to accounting for leases within Topic 840, Leases . The Company elected the practical expedient provided under ASU 2018-11, Leases (Topic 842) Targeted Improvements , which amended ASU 2016-02 to provide entities an optional transition practical expedient to adopt the new standard with a cumulative effect adjustment as of the beginning of the year of adoption with prior year comparative financial information and disclosures remaining as previously reported. As a result, no adjustments were made to the consolidated balance sheet prior to January 1, 2022 and amounts are reported in accordance with historical accounting under Topic 840, while the consolidated balance sheet as of March 31, 2022 is presented under Topic 842. The Company elected the package of practical expedients permitted under the transition guidance, which allowed it to carry forward historical lease classification, assessment on whether a contract was or contains a lease, and assessment of initial direct costs for any leases that existed prior to January 1, 2022. The Company also elected to combine its lease and non-lease components and to keep leases with an initial term of 12 months or less off the consolidated balance sheet and recognize the associated lease payments in the consolidated statements of operations on a straight-line basis over the lease term. For new required disclosures and further information see Note 8, Leases. Adoption of the new standard resulted in the recording of lease assets and lease liabilities of $4,534 thousand and $5,229 thousand, respectively, as of January 1, 2022. The transition did not have a material impact on the Company’s results of operations, cash flows or liquidity measures.

NET LOSS PER SHARE (Tables)

NET LOSS PER SHARE (Tables)	3 Months Ended
	Mar. 31, 2022
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Net Loss per Share Attributable to Common Shareholders	The following table presents the calculation of basic and diluted net loss per share attributable to common stockholders (in thousands, except per share data): Three Months Ended 2022 2021 Net loss attributable to common stockholders $ (5,709) $ (154,918) Weighted-average shares outstanding – Basic and Diluted 151,683,819 61,693,067 Net loss per share – Basic and Diluted $ (0.04) $ (2.51)
Schedule of Securities Excluded from Calculation of Diluted Weighted-Average Common Shares Outstanding	The following outstanding balances of common share equivalent securities have been excluded from the calculation of diluted weighted-average common shares outstanding because the effect is anti-dilutive for the periods presented: March 31, 2022 March 31, 2021 Stock options 3,707,113 4,379,633 RSUs 4,633,968 — Warrants 11,461,227 3,362,047 Number of securities outstanding 19,802,308 7,741,680

PREPAID EXPENSES AND OTHER CU_2

PREPAID EXPENSES AND OTHER CURRENT ASSETS (Tables)	3 Months Ended
	Mar. 31, 2022
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consist of the following (in thousands): March 31, 2022 December 31, 2021 Insurance $ 2,397 $ 3,482 Vendor advances 1,514 1,103 Other 495 259 Total prepaid expenses and other current assets $ 4,406 $ 4,844

PROPERTY AND EQUIPMENT, NET (Ta

PROPERTY AND EQUIPMENT, NET (Tables)	3 Months Ended
	Mar. 31, 2022
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment, net	Property and equipment, net consist of the following (in thousands): March 31, 2022 December 31, 2021 Machinery and equipment $ 2,910 $ 2,868 Furniture and fixtures 88 90 Leasehold improvements 1,030 746 Construction in process 7,944 2,517 Total property and equipment 11,972 6,221 Less accumulated depreciation (1,916) (1,720) Total property and equipment, net $ 10,056 $ 4,501

ACCRUED AND OTHER CURRENT LIA_2

ACCRUED AND OTHER CURRENT LIABILITIES (Tables)	3 Months Ended
	Mar. 31, 2022
Payables and Accruals [Abstract]
Schedule of Accrued and Other Current Liabilities	Accrued and other current liabilities consist of the following (in thousands): March 31, 2022 December 31, 2021 Payroll and related benefits $ 1,552 $ 1,876 Materials and related purchases 2,596 2,108 Deferred rent — 142 Professional and consulting fees 1,140 1,820 Other 1,327 541 Total accrued and other current liabilities $ 6,615 $ 6,487

LEASES (Tables)

LEASES (Tables)	3 Months Ended
	Mar. 31, 2022
Leases [Abstract]
Finance Lease Liability Maturities	As of March 31, 2022 future maturities of lease liabilities are as follows (in thousands): Operating Leases Finance Leases 2022 $ 1,222 $ 21 2023 1,670 30 2024 1,720 30 2025 983 30 2026 — 30 Thereafter — 7 Total minimum lease payments $ 5,595 $ 148 Less imputed interest (673) (25) Total $ 4,922 $ 123
Operating Lease Liability Maturities	As of March 31, 2022 future maturities of lease liabilities are as follows (in thousands): Operating Leases Finance Leases 2022 $ 1,222 $ 21 2023 1,670 30 2024 1,720 30 2025 983 30 2026 — 30 Thereafter — 7 Total minimum lease payments $ 5,595 $ 148 Less imputed interest (673) (25) Total $ 4,922 $ 123

BORROWINGS (Tables)

BORROWINGS (Tables)	3 Months Ended
	Mar. 31, 2022
Debt Disclosure [Abstract]
Schedule of Long Term Debt	Long term debt consists of the following (in thousands): March 31, 2022 December 31, 2021 Total notes payable $ 3,300 $ 3,769 Less current portion of notes payable 1,817 1,900 Notes payable, non-current $ 1,483 $ 1,869

LEGACY ESS REDEEMABLE CONVERT_2

LEGACY ESS REDEEMABLE CONVERTIBLE PREFERRED STOCK (Tables)	3 Months Ended
	Mar. 31, 2022
Temporary Equity Disclosure [Abstract]
Schedule of Warrants	The number of shares subject to and potential proceeds from the C-2 Redeemable Convertible Preferred Stock Purchase Agreement and related C-2 Warrants were as follows: As of May 7, 2021 Upon completion of the Business Combination Quantity Price Series C-2 Redeemable Convertible Preferred Stock Purchase Right 7,994,442 $ 2.00 Series C-2 Warrant exercisable upon completion of the Business Combination 21,159,364 $ 0.00007 The table below shows the common stock warrant activities during the three months ended March 31, 2022: December 31, 2021 Issued Exercised March 31, 2022 Earnout Warrants 583,334 — — 583,334 Public Warrants 7,377,913 — 20 7,377,893 Private Warrants 3,500,000 — — 3,500,000 Total Common Stock Warrants 11,461,247 — 20 11,461,227

COMMON STOCK WARRANTS (Tables)

COMMON STOCK WARRANTS (Tables)	3 Months Ended
	Mar. 31, 2022
Equity [Abstract]
Schedule of Common Stock Warrant Activity	The number of shares subject to and potential proceeds from the C-2 Redeemable Convertible Preferred Stock Purchase Agreement and related C-2 Warrants were as follows: As of May 7, 2021 Upon completion of the Business Combination Quantity Price Series C-2 Redeemable Convertible Preferred Stock Purchase Right 7,994,442 $ 2.00 Series C-2 Warrant exercisable upon completion of the Business Combination 21,159,364 $ 0.00007 The table below shows the common stock warrant activities during the three months ended March 31, 2022: December 31, 2021 Issued Exercised March 31, 2022 Earnout Warrants 583,334 — — 583,334 Public Warrants 7,377,913 — 20 7,377,893 Private Warrants 3,500,000 — — 3,500,000 Total Common Stock Warrants 11,461,247 — 20 11,461,227

STOCK-BASED COMPENSATION PLAN (

STOCK-BASED COMPENSATION PLAN (Tables)	3 Months Ended
	Mar. 31, 2022
Share-based Payment Arrangement [Abstract]
Schedule of Share-based Payment Arrangement, Option, Activity	Stock option and RSU activity, prices, and values during the three months ended March 31, 2022 is as follows (in thousands, except for share, per share, and contractual term data): Options Outstanding RSUs Number of Weighted Weighted Aggregate Number of plan shares outstanding Weighted average Balances as of December 31, 2021 3,796,530 $ 0.83 8.08 $ 40,274 3,392,153 $ 10.69 Options and RSUs granted 65,717 8.00 2,150,859 5.46 Options exercised and RSUs released (138,617) 0.30 (873,070) 11.12 Options and RSUs forfeited (16,517) 0.36 (35,974) 10.15 Balances as of March 31, 2022 3,707,113 $ 0.98 8.03 $ 17,012 4,633,968 $ 8.82 Options vested and exercisable - December 31, 2021 1,827,374 $ 0.31 7.20 $ 20,337 Options vested and exercisable - March 31, 2022 1,626,013 $ 0.56 7.41 $ 8,140
Schedule of Share-based Payment Arrangement, Restricted Stock Unit, Activity	Stock option and RSU activity, prices, and values during the three months ended March 31, 2022 is as follows (in thousands, except for share, per share, and contractual term data): Options Outstanding RSUs Number of Weighted Weighted Aggregate Number of plan shares outstanding Weighted average Balances as of December 31, 2021 3,796,530 $ 0.83 8.08 $ 40,274 3,392,153 $ 10.69 Options and RSUs granted 65,717 8.00 2,150,859 5.46 Options exercised and RSUs released (138,617) 0.30 (873,070) 11.12 Options and RSUs forfeited (16,517) 0.36 (35,974) 10.15 Balances as of March 31, 2022 3,707,113 $ 0.98 8.03 $ 17,012 4,633,968 $ 8.82 Options vested and exercisable - December 31, 2021 1,827,374 $ 0.31 7.20 $ 20,337 Options vested and exercisable - March 31, 2022 1,626,013 $ 0.56 7.41 $ 8,140
Schedule of Valuation Assumptions	In accordance with ASC 718, Compensation – Stock Compensation , the fair value of each option grant has been estimated as of the date of grant using the following weighted average assumptions: Three Months Ended March 31, 2022 2021 Risk-free rate 1.64 % 0.75 % Expected dividends — — Expected term 6 years 6 years Expected volatility 73.95 % 74.80 %
Schedule of Stock-Based Compensation	The following table presents the amount of stock-based compensation related to stock-based awards to employees on the Company’s consolidated statements of operations and comprehensive loss (in thousands): Three Months Ended March 31, 2022 2021 Research and development $ 587 $ 64 Sales and marketing 54 16 General and administrative 2,119 49 Total stock-based compensation $ 2,760 $ 129

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	3 Months Ended
	Mar. 31, 2022
Fair Value Disclosures [Abstract]
Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis	The following table presents the Company’s fair value hierarchy for its financial assets and liabilities measured at fair value on a recurring basis (in thousands): March 31, 2022 Level 1 Level 2 Level 3 Total Assets: Cash equivalents and restricted cash: Money market funds $ 211,369 $ — $ — $ 211,369 Certificate of deposit — 75 — 75 Total assets $ 211,369 $ 75 $ — $ 211,444 Liabilities: Earnout warrant liabilities $ — $ 636 $ — $ 636 Public common stock warrants 8,042 — — 8,042 Private common stock warrants — 3,815 — 3,815 Total liabilities $ 8,042 $ 4,451 $ — $ 12,493 December 31, 2021 Level 1 Level 2 Level 3 Total Assets: Cash equivalents and restricted cash: Money market funds $ 237,897 $ — $ — $ 237,897 Certificate of deposit — 125 — 125 Total assets $ 237,897 $ 125 $ — $ 238,022 Liabilities: Earnout warrant liabilities $ — $ 1,476 $ — $ 1,476 Public common stock warrants 18,666 — — 18,666 Private common stock warrants — 8,855 — 8,855 Total liabilities $ 18,666 $ 10,331 $ — $ 28,997
Schedule of Changes in Fair Value Liabilities on Recurring Basis	The following table sets forth a summary of changes in the fair value of the Company’s Level 3 liabilities at fair value on a recurring basis (in thousands): Three Months Ended March 31, 2022 2021 Warrant liabilities: Beginning balance December 31 $ — $ 3,329 Change in fair value — 8,426 Fair value of warrants issued — 5,096 Fair value of warrants exercised — (356) Ending balance March 31 — 16,495 Series C-2 Convertible Preferred Stock Issuance Right liability: Beginning balance December 31 — 22,911 Change in fair value — 138,141 Fair value of derivatives extinguished — (23,152) Ending balance March 31 — 137,900 Total $ — $ 154,395

DESCRITPION OF BUSINESS AND B_2

DESCRITPION OF BUSINESS AND BASIS OF PRESENTATION (Details)	Oct. 08, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Recapitalization exchange ratio	0.0147

SIGNIFICANT ACCOUNTING POLICI_3

SIGNIFICANT ACCOUNTING POLICIES (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Jan. 01, 2022	Dec. 31, 2021
Significant Accounting Policies [Line Items]
Operating lease right-of-use assets	$ 4,260			$ 0
Total	$ 4,922
Accounting Standards Update 2016-02
Significant Accounting Policies [Line Items]
Operating lease right-of-use assets			$ 4,534
Total			$ 5,229
Stock options
Significant Accounting Policies [Line Items]
Expected dividends	0.00%	0.00%

BUSINESS COMBINATION (Details)

BUSINESS COMBINATION (Details) - $ / shares	Nov. 09, 2021	Oct. 08, 2021	Mar. 31, 2022	Dec. 31, 2021	Oct. 07, 2021
Business Acquisition [Line Items]
Common stock, par value (in USD per share)		$ 0.0001	$ 0.0001	$ 0.0001
Preferred stock, par value (in USD per share)		$ 0.0001	$ 0.0001	$ 0.0001
Common and preferred stock authorized (in shares)		2,200,000,000
Common stock, shares authorized (in shares)		2,000,000,000	2,000,000,000	2,000,000,000
Preferred stock, shares authorized (in shares)		200,000,000	200,000,000	200,000,000
Common Stock
Business Acquisition [Line Items]
Shares issuable under contingent consideration (in shares)		16,500,000
Legacy ESS
Business Acquisition [Line Items]
Common stock, par value (in USD per share)					$ 0.0001
Preferred stock, par value (in USD per share)					$ 0.0001
Legacy ESS | Common Stock
Business Acquisition [Line Items]
Shares issued upon completion of milestones (in shares)	15,674,965
Legacy ESS Shareholders
Business Acquisition [Line Items]
Shares issued (in shares)		99,700,326
Legacy ESS Shareholders | Transaction Expense Adjustment
Business Acquisition [Line Items]
Shares issued (in shares)		125,958

NET LOSS PER SHARE - Schedule o

NET LOSS PER SHARE - Schedule of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Earnings Per Share [Abstract]
Net loss to common stockholders, diluted	$ (5,709)	$ (154,918)
Net loss to common stockholders, basic	$ (5,709)	$ (154,918)
Weighted average shares used in per share calculation, basic (in shares)	151,683,819	61,693,067
Weighted average shares used in per share calculation, diluted (in shares)	151,683,819	61,693,067
Net loss per share, diluted (in USD per share)	$ (0.04)	$ (2.51)
Net loss per share, basic (in USD per share)	$ (0.04)	$ (2.51)

NET LOSS PER SHARE - Schedule A

NET LOSS PER SHARE - Schedule Antidilutive Securities (Details) - shares	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of securities outstanding (in shares)	19,802,308	7,741,680
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of securities outstanding (in shares)	3,707,113	4,379,633
RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of securities outstanding (in shares)	4,633,968	0
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of securities outstanding (in shares)	11,461,227	3,362,047

PREPAID EXPENSES AND OTHER CU_3

PREPAID EXPENSES AND OTHER CURRENT ASSETS (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Insurance	$ 2,397	$ 3,482
Vendor advances	1,514	1,103
Other	495	259
Total prepaid expenses and other current assets	$ 4,406	$ 4,844

PROPERTY AND EQUIPMENT, NET (De

PROPERTY AND EQUIPMENT, NET (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 11,972		$ 6,221
Less accumulated depreciation	(1,916)		(1,720)
Total property and equipment, net	10,056		4,501
Depreciation expense	196	$ 130
Machinery and equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	2,910		2,868
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property and equipment	88		90
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment	1,030		746
Construction in process
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 7,944		$ 2,517

ACCRUED AND OTHER CURRENT LIA_3

ACCRUED AND OTHER CURRENT LIABILITIES (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Payables and Accruals [Abstract]
Payroll and related benefits	$ 1,552	$ 1,876
Materials and related purchases	2,596	2,108
Deferred rent	0	142
Professional and consulting fees	1,140	1,820
Other	1,327	541
Total accrued and other current liabilities	$ 6,615	$ 6,487

LEASES - Narrative (Details)

LEASES - Narrative (Details)	3 Months Ended
	Mar. 31, 2022USD ($)
Leases [Abstract]
Short-term lease cost	$ 0
Renewal term	60 months
Operating lease cost	$ 371,000
Operating lease, weighted average remaining term	3 years 4 months 24 days
Operating lease, weighted average discount rate	7.50%
Finance lease, weighted average remaining term	4 years 10 months 24 days
Operating lease, weighted average discount rate	7.50%

LEASES- Maturities of Operating

LEASES- Maturities of Operating and Financing Lease Liabilities (Details) $ in Thousands	Mar. 31, 2022USD ($)
Operating Leases
2022	$ 1,222
2023	1,670
2024	1,720
2025	983
2026	0
Thereafter	0
Total minimum lease payments	5,595
Less imputed interest	(673)
Total	4,922
Finance Leases
2022	21
2023	30
2024	30
2025	30
2026	30
Thereafter	7
Total minimum lease payments	148
Less imputed interest	(25)
Total	$ 123

BORROWINGS - Schedule of Long T

BORROWINGS - Schedule of Long Term Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Debt Disclosure [Abstract]
Total notes payable	$ 3,300	$ 3,769
Less current portion of notes payable	1,817	1,900
Notes payable, non-current	$ 1,483	$ 1,869

BORROWINGS - Narrative (Details

BORROWINGS - Narrative (Details) - Notes Payable $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2018USD ($)
Debt Instrument [Line Items]
Debt amount			$ 4,000	$ 1,000
Gain (loss) on extinguishment of debt		$ (62)
Percent change in present value of cash flows			0.10
Effective interest rate	3.00%
Prime
Debt Instrument [Line Items]
Spread on interest rate	0.50%

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Other Commitments [Line Items]
Restricted certificate of deposit	$ 75
Noncancellable Agreement
Other Commitments [Line Items]
Noncancelable purchase commitments	23,344		$ 10,160
Cancellable Agreement
Other Commitments [Line Items]
Noncancelable purchase commitments	3,539		10,446
Letter of Credit | First Republic Bank
Other Commitments [Line Items]
Standby letter of credit	725		$ 725
Draws against letter of credit	$ 0	$ 0

LEGACY ESS REDEEMABLE CONVERT_3

LEGACY ESS REDEEMABLE CONVERTIBLE PREFERRED STOCK - Narrative (Details) $ / shares in Units, $ in Thousands	Oct. 08, 2021USD ($)$ / shares	Oct. 07, 2021USD ($)$ / sharesshares	Mar. 31, 2021USD ($)$ / sharesshares	Mar. 31, 2022USD ($)shares	Mar. 31, 2021USD ($)$ / shares	Dec. 31, 2021USD ($)shares	May 07, 2021$ / shares	Dec. 31, 2020USD ($)
Temporary Equity [Line Items]
Recapitalization exchange ratio	0.0147
Fair value of temporary equity			$ 0	$ 0	$ 0	$ 0		$ 0
Value of share issued					29,516
Warrants issued (in shares) | shares				0
Warrants exercised (in shares) | shares				20
Increase in derivative liability				$ 0	(138,141)
Warrants (in shares) | shares				11,461,227		11,461,247
Series C-2 Redeemable Convertible Preferred Stock Purchase Rights And Warrants
Temporary Equity [Line Items]
Stock issuance costs	$ 439
Proceeds from transaction	$ 15,559
Legacy ESS
Temporary Equity [Line Items]
Transaction value			$ 34,613		$ 34,613
Warrants term		10 years
Legacy ESS | Series C-2 Redeemable Convertible Preferred Stock Purchase Right
Temporary Equity [Line Items]
Fair value of temporary equity		$ 11,379
Warrants issued (in shares) | shares			861,896
Warrants exercised (in shares) | shares			5,746,003
Warrant exercise price (in USD per share) | $ / shares			$ 0.0001		$ 0.0001
Legacy ESS | Series C-2 Redeemable Convertible Preferred Stock Warrants
Temporary Equity [Line Items]
Warrant exercise price (in USD per share) | $ / shares							$ 0.00007
Warrants term		10 years
Legacy ESS | Series C-2 Redeemable Convertible Preferred Stock Warrants | Minimum
Temporary Equity [Line Items]
Warrant exercise price (in USD per share) | $ / shares		$ 0.00007
Legacy ESS | Series C-2 Redeemable Convertible Preferred Stock Warrants | Maximum
Temporary Equity [Line Items]
Warrant exercise price (in USD per share) | $ / shares		$ 1.25
Legacy ESS | Series B Redeemable Convertible Preferred Stock Warrants
Temporary Equity [Line Items]
Warrants (in shares) | shares		100,161
Legacy ESS | Series B Redeemable Convertible Preferred Stock Warrants | Minimum
Temporary Equity [Line Items]
Warrant exercise price (in USD per share) | $ / shares		$ 0.0007
Legacy ESS | Series B Redeemable Convertible Preferred Stock Warrants | Maximum
Temporary Equity [Line Items]
Warrant exercise price (in USD per share) | $ / shares		$ 0.83
Legacy ESS | Series C-1 Redeemable Convertible Preferred Stock Warrants
Temporary Equity [Line Items]
Warrants term		10 years
Legacy ESS | Series C-1 Redeemable Convertible Preferred Stock Warrants | Minimum
Temporary Equity [Line Items]
Warrant exercise price (in USD per share) | $ / shares		$ 0.00007
Legacy ESS | Series C-1 Redeemable Convertible Preferred Stock Warrants | Maximum
Temporary Equity [Line Items]
Warrant exercise price (in USD per share) | $ / shares		1.25
Legacy ESS | Common Stock Warrants
Temporary Equity [Line Items]
Warrant exercise price (in USD per share) | $ / shares		$ 0.0007
Common Stock
Temporary Equity [Line Items]
Conversion of convertible shares (in shares) | shares		57,104,332
Price per share (in USD per share) | $ / shares	$ 11.50
Series C-2 Redeemable Convertible Preferred Stock | Legacy ESS
Temporary Equity [Line Items]
Committed funding amount		$ 79,999
Committed purchase of shares (in shares) | shares		39,971,716
Committed price per share (in USD per share) | $ / shares		$ 2
Shares issued (in shares) | shares			5,746,003
Price per share (in USD per share) | $ / shares			$ 2		$ 2
Value of share issued			$ 11,500
Stock issuance costs			39
Derivative liability			23,152		$ 23,152
Transaction value			29,516		29,516
Warrants | Legacy ESS
Temporary Equity [Line Items]
Transaction value			$ 5,096		$ 5,096

LEGACY ESS REDEEMABLE CONVERT_4

LEGACY ESS REDEEMABLE CONVERTIBLE PREFERRED STOCK - Schedule of Rights and Warrants (Details) - Legacy ESS	May 07, 2021$ / sharesshares
Series C-2 Redeemable Convertible Preferred Stock Purchase Right
Class of Warrant or Right [Line Items]
Shares issued (in shares) | shares	7,994,442
Price per share (in USD per share) | $ / shares	$ 2
Series C-2 Warrant exercisable upon completion of the Business Combination
Class of Warrant or Right [Line Items]
Shares issued (in shares) | shares	21,159,364
Price per share (in USD per share) | $ / shares	$ 0.00007

COMMON STOCK WARRANTS - Narrati

COMMON STOCK WARRANTS - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	Oct. 08, 2021	Sep. 21, 2020	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021	Nov. 09, 2021
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)			11,461,227		11,461,247
Warrants issued (in shares)			0
Warrants exercised (in shares)			20
Net decrease to warrant liabilities			$ (15,664)	$ 8,426
Redemption Scenario, Two
Class of Warrant or Right [Line Items]
Price of common stock triggering redemption of warrants (in USD per share)			$ 10
Price of common stock with trading days threshold, triggering redemption of warrants (in USD per share)			$ 10
Trading days triggering redemption of warrants			20 days
Consecutive trading day period			30 days
Common Stock
Class of Warrant or Right [Line Items]
Price per share (in USD per share)	$ 11.50
Common Stock | STWO
Class of Warrant or Right [Line Items]
Price per share (in USD per share)		$ 11.50
Common Stock | Public Warrant Holders | STWO
Class of Warrant or Right [Line Items]
Issuance of shares (in shares)		1
Common Stock | Private Warrant Holders
Class of Warrant or Right [Line Items]
Issuance of shares (in shares)	1
Common Stock | Earnout Warrant Holders
Class of Warrant or Right [Line Items]
Issuance of shares (in shares)	1
Private common stock warrants | Private Placement | STWO | STWO's Sponsor
Class of Warrant or Right [Line Items]
Shares issued (in shares)		4,666,667
Public common stock warrants
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)			7,377,893		7,377,913
Warrants issued (in shares)			0
Warrants exercised (in shares)			20
Net decrease to warrant liabilities			$ 10,624
Public common stock warrants | STWO
Class of Warrant or Right [Line Items]
Warrants issued (in shares)	8,333,287
Warrants term		5 years
Public common stock warrants | Redemption Scenario, One
Class of Warrant or Right [Line Items]
Redemption price per share (in USD per share)			$ 0.01
Price of common stock triggering redemption of warrants (in USD per share)			18
Price of common stock with trading days threshold, triggering redemption of warrants (in USD per share)			$ 10
Trading days triggering redemption of warrants			20 days
Consecutive trading day period			30 days
Public common stock warrants | Redemption Scenario, Two
Class of Warrant or Right [Line Items]
Redemption price per share (in USD per share)			$ 0.10
Public common stock warrants | Redemption Scenario, Three
Class of Warrant or Right [Line Items]
Price of common stock triggering redemption of warrants (in USD per share)			18
Price of common stock with trading days threshold, triggering redemption of warrants (in USD per share)			$ 10
Trading days triggering redemption of warrants			20 days
Consecutive trading day period			30 days
Private common stock warrants
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)	4,083,334		3,500,000		3,500,000
Warrants issued (in shares)			0
Warrants vested (in shares)	3,500,000
Warrants exercised (in shares)			0
Net decrease to warrant liabilities			$ 5,040
Private common stock warrants | STWO's Sponsor
Class of Warrant or Right [Line Items]
Warrants forfeited (in shares)	583,333
Earnout Warrants
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)			583,334		583,334
Warrants issued (in shares)			0
Warrants vested (in shares)						583,334
Warrants exercised (in shares)			0
Net decrease to warrant liabilities			$ 840

COMMON STOCK WARRANTS - Schedul

COMMON STOCK WARRANTS - Schedule of Common Stock Warrant Activity (Details) - shares	Oct. 08, 2021	Mar. 31, 2022
Class of Warrant or Right [Roll Forward]
Warrants or rights at beginning of period (in shares)		11,461,247
Warrants issued (in shares)		0
Warrants exercised (in shares)		20
Warrants or rights at end of period (in shares)		11,461,227
Earnout Warrants
Class of Warrant or Right [Roll Forward]
Warrants or rights at beginning of period (in shares)		583,334
Warrants issued (in shares)		0
Warrants exercised (in shares)		0
Warrants or rights at end of period (in shares)		583,334
Public Warrants
Class of Warrant or Right [Roll Forward]
Warrants or rights at beginning of period (in shares)		7,377,913
Warrants issued (in shares)		0
Warrants exercised (in shares)		20
Warrants or rights at end of period (in shares)		7,377,893
Private Warrants
Class of Warrant or Right [Roll Forward]
Warrants or rights at beginning of period (in shares)		3,500,000
Warrants issued (in shares)		0
Warrants exercised (in shares)		0
Warrants or rights at end of period (in shares)	4,083,334	3,500,000

STOCK-BASED COMPENSATION PLAN -

STOCK-BASED COMPENSATION PLAN - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Potential increase of shares authorized (in shares)	15,260,000
Percentage of potential increase of shares authorized	5.00%
Shares authorized for issuance (in shares)	17,610,000
Award vesting period	3 years
Shares available for future grant (in shares)	13,021,489
Unamortized stock-based compensation costs	$ 24,071
Weighted average period of recognition for unamortized stock-based compensation costs	3 years 1 month 9 days
Stock Appreciation Rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)	0
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)	0
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)	4,633,968	3,392,153
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share expiration period	10 years
Non-qualified Stock Options (NSOs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)	0
Incentive Stock Options (ISOs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)	0

STOCK-BASED COMPENSATION PLAN_2

STOCK-BASED COMPENSATION PLAN - Schedule of Share-based Payment Arrangement, Option and RSU Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Options Outstanding
Options outstanding at beginning of period (in shares)	3,796,530
Options granted (in shares)	65,717
Options released (in shares)	(138,617)
Options forfeited (in shares)	(16,517)
Options outstanding at end of period (in shares)	3,707,113	3,796,530
Options vested and exercisable (in shares)	1,626,013	1,827,374
Weighted average exercise price
Weighted average exercise price of options outstanding at beginning of period (in USD per share)	$ 0.83
Weighted average exercise price of options granted (in USD per share)	8
Weighted average exercise price of options released (in USD per share)	0.30
Weighted average exercise price of options forfeited (in USD per share)	0.36
Weighted average exercise price of options outstanding at end of period (in USD per share)	0.98	$ 0.83
Weighted average exercise price of options vested and exercisable (in USD per share)	$ 0.56	$ 0.31
Options, Additional Disclosures
Weighted average remaining contractual term of options outstanding	8 years 10 days	8 years 29 days
Weighted average remaining contractual term of options vested and exercisable	7 years 4 months 28 days	7 years 2 months 12 days
Aggregate intrinsic value of options outstanding	$ 17,012	$ 40,274
Aggregate intrinsic value of options vested and exercisable	$ 8,140	$ 20,337
RSUs
RSUs
Units outstanding at beginning of period (in shares)	3,392,153
Units granted (in shares)	2,150,859
Units released (in shares)	(873,070)
Units forfeited (in shares)	(35,974)
Units outstanding at end of period (in shares)	4,633,968	3,392,153
Weighted average grant date fair value per Share
Weighted average grant date fair value per share of units outstanding at beginning of period (in USD per share)	$ 10.69
Weighted average grant date fair value per share of units granted (in USD per share)	5.46
Weighted average grant date fair value per share of units released (in USD per share)	11.12
Weighted average grant date fair value per share of units forfeited (in USD per share)	10.15
Weighted average grant date fair value per share of units outstanding at end of period (in USD per share)	$ 8.82	$ 10.69

STOCK-BASED COMPENSATION PLAN_3

STOCK-BASED COMPENSATION PLAN - Schedule of Valuation Assumptions (Details) - Stock options	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free rate	1.64%	0.75%
Expected dividends	0.00%	0.00%
Expected term	6 years	6 years
Expected volatility	73.95%	74.80%

STOCK-BASED COMPENSATION PLAN_4

STOCK-BASED COMPENSATION PLAN - Schedule of Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	$ 2,760	$ 129
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	587	64
Sales and marketing
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	54	16
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	$ 2,119	$ 49

FAIR VALUE MEASUREMENTS - Sched

FAIR VALUE MEASUREMENTS - Schedule of Assets and Liabilities on Recurring Basis (Details) - Fair Value, Recurring - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Assets, Fair Value Disclosure [Abstract]
Total assets	$ 211,444	$ 238,022
Liabilities, Fair Value Disclosure [Abstract]
Earnout warrant liabilities	636
Earnout warrant liabilities		1,476
Total liabilities	12,493	28,997
Public common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	8,042	18,666
Private common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	3,815	8,855
Money market funds
Assets, Fair Value Disclosure [Abstract]
Cash equivalents and restricted cash:	211,369	237,897
Certificate of deposit
Assets, Fair Value Disclosure [Abstract]
Cash equivalents and restricted cash:	75	125
Level 1
Assets, Fair Value Disclosure [Abstract]
Total assets	211,369	237,897
Liabilities, Fair Value Disclosure [Abstract]
Earnout warrant liabilities	0
Earnout warrant liabilities		0
Total liabilities	8,042	18,666
Level 1 | Public common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	8,042	18,666
Level 1 | Private common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	0	0
Level 1 | Money market funds
Assets, Fair Value Disclosure [Abstract]
Cash equivalents and restricted cash:	211,369	237,897
Level 1 | Certificate of deposit
Assets, Fair Value Disclosure [Abstract]
Cash equivalents and restricted cash:	0	0
Level 2
Assets, Fair Value Disclosure [Abstract]
Total assets	75	125
Liabilities, Fair Value Disclosure [Abstract]
Earnout warrant liabilities	636
Earnout warrant liabilities		1,476
Total liabilities	4,451	10,331
Level 2 | Public common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	0	0
Level 2 | Private common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	3,815	8,855
Level 2 | Money market funds
Assets, Fair Value Disclosure [Abstract]
Cash equivalents and restricted cash:	0	0
Level 2 | Certificate of deposit
Assets, Fair Value Disclosure [Abstract]
Cash equivalents and restricted cash:	75	125
Level 3
Assets, Fair Value Disclosure [Abstract]
Total assets	0	0
Liabilities, Fair Value Disclosure [Abstract]
Earnout warrant liabilities	0
Earnout warrant liabilities		0
Total liabilities	0	0
Level 3 | Public common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	0	0
Level 3 | Private common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Common stock warrants	0	0
Level 3 | Money market funds
Assets, Fair Value Disclosure [Abstract]
Cash equivalents and restricted cash:	0	0
Level 3 | Certificate of deposit
Assets, Fair Value Disclosure [Abstract]
Cash equivalents and restricted cash:	$ 0	$ 0

FAIR VALUE MEASUREMENTS - Sch_2

FAIR VALUE MEASUREMENTS - Schedule of Changes in Fair Value Liabilities on Recurring Basis (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at end of period	$ 0	$ 154,395
Warrant liabilities
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	0	3,329
Fair value of warrants issued	0	5,096
Change in fair value	0	8,426
Fair value of warrants exercised	0	(356)
Balance at end of period	0	16,495
Redeemable Convertible Preferred Stock
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	0	22,911
Change in fair value	0	138,141
Fair value of derivatives extinguished	0	(23,152)
Balance at end of period	$ 0	$ 137,900

INCOME TAXES - Narrative (Detai

INCOME TAXES - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Income tax expense provision	$ 0	$ 0

RELATED PARTY TRANSACTIONS (Det

RELATED PARTY TRANSACTIONS (Details) - USD ($) $ in Thousands	Nov. 09, 2021	Mar. 31, 2022	Dec. 31, 2021
Related Party Transaction [Line Items]
Deferred revenue		$ 6,859	$ 3,663
Common Stock | Legacy ESS
Related Party Transaction [Line Items]
Shares issued to related parties (in shares)	15,674,965
Related parties | Common Stock | Legacy ESS
Related Party Transaction [Line Items]
Shares issued to related parties (in shares)	6,707,318
Energy Warehouse Sales
Related Party Transaction [Line Items]
Accounts receivable from related party			66
Deferred revenue		$ 237	$ 171