ESS Tech (GWH) 10-Q 14 Aug 24 2024 Q2 Quarterly report Financial data

Cover

Cover - shares	6 Months Ended
	Jun. 30, 2024	Aug. 09, 2024
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2024
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		176,825,064
Entity Central Index Key	0001819438
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q2
Current Fiscal Year End Date	--12-31
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
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

Condensed Balance Sheets (unaud

Condensed Balance Sheets (unaudited) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 36,744	$ 20,165
Restricted cash, current	906	1,373
Accounts receivable, net	981	1,990
Short-Term Investments	37,695	87,899
Inventory	4,425	3,366
Prepaid expenses and other current assets	3,908	3,305
Total current assets	84,659	118,098
Property and equipment, net	17,758	16,266
Intangible assets, net	4,790	4,923
Operating lease right-of-use assets	2,195	2,167
Restricted cash, non-current	946	945
Other non-current assets	785	833
Total assets	111,133	143,232
Current liabilities:
Accounts payable	5,833	2,755
Accrued and other current liabilities	9,669	10,755
Accrued product warranties	3,240	2,129
Operating lease liabilities, current	1,572	1,581
Deferred revenue, current	5,689	2,546
Total current liabilities	26,003	19,766
Operating lease liabilities, non-current	884	957
Deferred revenue, non-current	14,400
Common stock warrant liabilities	802	917
Total liabilities	42,089	39,875
Commitments and contingencies (Note 8)
Stockholders’ equity:
Preferred stock ($0.0000 par value; 200,000 shares authorized, none issued and outstanding as of June 30, 2024 and December 31, 2023)	0	0
Common stock ($0.0001 par value; 2,000,000,000 shares authorized, 176,822,039 and 174,211,911 shares issued and outstanding as of June 30, 2024 and December 31, 2023, respectively)	18	18
Additional paid-in capital	805,433	799,496
Accumulated deficit	(736,407)	(696,157)
Total stockholders’ equity	69,044	103,357
Total liabilities and stockholders’ equity	111,133	143,232
Nonrelated party
Current liabilities:
Deferred revenue, non-current	0	3,835
Related party
Current liabilities:
Deferred revenue, non-current	$ 14,400	$ 14,400

Condensed Balance Sheets (una_2

Condensed Balance Sheets (unaudited) (Parenthetical) - $ / shares	Jun. 30, 2024	Dec. 31, 2023
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)	176,822,039	174,211,911
Common stock, shares outstanding (in shares)	176,822,039	174,211,911

Condensed Statements of Operati

Condensed Statements of Operations and Comprehensive Loss (unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Revenue:
Total revenue	$ 348	$ 2,827	$ 3,086	$ 3,199
Cost of revenue	11,748	0	22,874	0
Gross profit (loss)	(11,400)	2,827	(19,788)	3,199
Operating expenses:
Research and development	2,836	19,450	6,382	37,181
Sales and marketing	2,711	1,739	4,745	3,592
General and administrative	6,178	5,845	11,704	11,132
Total operating expenses	11,725	27,034	22,831	51,905
Loss from operations	(23,125)	(24,207)	(42,619)	(48,706)
Other income (expenses), net:
Interest income, net	1,052	1,330	2,291	2,582
Gain (loss) on revaluation of common stock warrant liabilities	115	(115)	115	573
Other income (expense), net	18	63	(37)	721
Total other income, net	1,185	1,278	2,369	3,876
Net loss to common stockholders	(21,940)	(22,929)	(40,250)	(44,830)
Comprehensive loss to common stockholders	$ (21,940)	$ (22,929)	$ (40,250)	$ (44,830)
Net loss per share - basic (in USD per share)	$ (0.12)	$ (0.15)	$ (0.23)	$ (0.29)
Net loss per share - diluted (in USD per share)	$ (0.12)	$ (0.15)	$ (0.23)	$ (0.29)
Weighted average shares used in per share calculation, basic (in shares)	175,758,584	154,900,330	175,136,561	154,514,265
Weighted average shares used in per share calculation, diluted (in shares)	175,758,584	154,900,330	175,136,561	154,514,265
Nonrelated party
Revenue:
Total revenue	$ 342	$ 2,826	$ 2,556	$ 3,197
Related party
Revenue:
Total revenue	$ 6	$ 1	$ 530	$ 2

Condensed Statements of Stockho

Condensed Statements of Stockholders' Equity (unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit
Balance at beginning of period (in shares) at Dec. 31, 2022		153,821,339
Balance at beginning of period at Dec. 31, 2022	$ 136,974	$ 16	$ 755,537	$ (618,579)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under stock-based compensation plans, net of stock withheld for taxes (in shares)		523,591
Issuance of common stock under stock-based compensation plans, net of stock withheld for taxes	104		104
Stock-based compensation expense	2,059		2,059
Net loss	(21,901)			(21,901)
Balance at end of period (in shares) at Mar. 31, 2023		154,344,930
Balance at end of period at Mar. 31, 2023	117,236	$ 16	757,700	(640,480)
Balance at beginning of period (in shares) at Dec. 31, 2022		153,821,339
Balance at beginning of period at Dec. 31, 2022	136,974	$ 16	755,537	(618,579)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(44,830)
Balance at end of period (in shares) at Jun. 30, 2023		155,570,588
Balance at end of period at Jun. 30, 2023	97,300	$ 16	760,693	(663,409)
Balance at beginning of period (in shares) at Mar. 31, 2023		154,344,930
Balance at beginning of period at Mar. 31, 2023	117,236	$ 16	757,700	(640,480)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	2,725		2,725
Issuance of common stock under stock-based compensation plans, net of stock withheld for taxes (in shares)		1,225,658
Issuance of common stock under stock-based compensation plans, net of stock withheld for taxes	268		268
Net loss	(22,929)			(22,929)
Balance at end of period (in shares) at Jun. 30, 2023		155,570,588
Balance at end of period at Jun. 30, 2023	$ 97,300	$ 16	760,693	(663,409)
Balance at beginning of period (in shares) at Dec. 31, 2023	174,211,911	174,211,911
Balance at beginning of period at Dec. 31, 2023	$ 103,357	$ 18	799,496	(696,157)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under stock-based compensation plans, net of stock withheld for taxes (in shares)		686,175
Issuance of common stock under stock-based compensation plans, net of stock withheld for taxes	(81)		(81)
Stock-based compensation expense	2,854		2,854
Net loss	(18,310)			(18,310)
Balance at end of period (in shares) at Mar. 31, 2024		174,898,086
Balance at end of period at Mar. 31, 2024	$ 87,820	$ 18	802,269	(714,467)
Balance at beginning of period (in shares) at Dec. 31, 2023	174,211,911	174,211,911
Balance at beginning of period at Dec. 31, 2023	$ 103,357	$ 18	799,496	(696,157)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	$ (40,250)
Balance at end of period (in shares) at Jun. 30, 2024	176,822,039	176,822,039
Balance at end of period at Jun. 30, 2024	$ 69,044	$ 18	805,433	(736,407)
Balance at beginning of period (in shares) at Mar. 31, 2024		174,898,086
Balance at beginning of period at Mar. 31, 2024	87,820	$ 18	802,269	(714,467)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	3,026		3,026
Issuance of common stock under stock-based compensation plans, net of stock withheld for taxes (in shares)		1,923,953
Issuance of common stock under stock-based compensation plans, net of stock withheld for taxes	138		138
Net loss	$ (21,940)			(21,940)
Balance at end of period (in shares) at Jun. 30, 2024	176,822,039	176,822,039
Balance at end of period at Jun. 30, 2024	$ 69,044	$ 18	$ 805,433	$ (736,407)

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Cash flows from operating activities:
Net loss	$ (40,250)	$ (44,830)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	2,521	2,105
Non-cash interest income	(1,573)	(1,487)
Non-cash lease expense	658	604
Stock-based compensation expense	5,880	4,784
Inventory write-down and losses on noncancellable purchase commitments	1,530	0
Change in fair value of common stock warrant liabilities	(115)	(573)
Other non-cash (income) expenses, net	25	(33)
Changes in operating assets and liabilities:
Accounts receivable, net	1,526	4,653
Inventory	(2,875)	0
Prepaid expenses and other current assets	(555)	2,561
Accounts payable	1,925	(664)
Accrued and other current liabilities	(1,962)	(4,234)
Accrued product warranties	1,111	3,460
Deferred revenue	(1,209)	(3,189)
Operating lease liabilities	(768)	(689)
Net cash used in operating activities	(34,131)	(37,532)
Cash flows from investing activities:
Purchases of property and equipment	(1,565)	(3,440)
Maturities and purchases of short-term investments, net	51,752	37,363
Net cash provided by investing activities	50,187	33,923
Cash flows from financing activities:
Payments on notes payable	0	(800)
Proceeds from stock options exercised	21	122
Repurchase of shares from employees for income tax withholding purposes	(178)	(82)
Proceeds from contributions to Employee Stock Purchase Plan	214	332
Other, net	0	(14)
Net cash provided by (used in) financing activities	57	(442)
Net change in cash, cash equivalents and restricted cash	16,113	(4,051)
Cash, cash equivalents and restricted cash, beginning of period	22,483	36,655
Cash, cash equivalents and restricted cash, end of period	38,596	32,604
Supplemental disclosures of cash flow information:
Cash paid for operating leases included in cash used in operating activities	874	827
Non-cash investing and financing transactions:
Purchase of property and equipment included in accounts payable and accrued and other current liabilities	1,970	931
Adjustment to right-of-use assets from lease modification	686	0
Transfers between inventory and property and equipment, net	1,051	0
Cash and cash equivalents	36,744	30,287
Restricted cash, current	906	1,373
Restricted cash, non-current	946	944
Total cash, cash equivalents and restricted cash shown in the condensed statements of cash flows	$ 38,596	$ 32,604

DESCRITPION OF BUSINESS AND BAS

DESCRITPION OF BUSINESS AND BASIS OF PRESENTATION	6 Months Ended
	Jun. 30, 2024
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 predominantly using earth-abundant materials. 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 business combination. On October 8, 2021 (the “Closing Date”), the Company consummated a business combination (the “Business Combination”) pursuant to 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”), wherein Merger Sub merged with and into Legacy ESS, with Legacy ESS surviving as a wholly owned subsidiary of STWO. On the Closing Date, STWO changed its name from “ACON S2 Acquisition Corp.” to “ESS Tech, Inc.”, and its shares of common stock and warrants for shares of common stock commenced trading on the New York Stock Exchange under the ticker symbols “GWH” and “GWH.W,” respectively. On March 31, 2024, Legacy ESS merged with ESS Tech, Inc. leaving ESS Tech, Inc. as the sole remaining legal entity. As of April 1, 2024, the Company does not have any subsidiaries. Basis of Presentation —The accompanying condensed financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). Condensed Financial Statements —The accompanying unaudited condensed 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 U.S. Securities and Exchange Commission (“SEC”) for interim financial reporting. Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. The condensed financial statements reflect all normal and recurring adjustments that are, in the opinion of the Company’s management, necessary in order to make the condensed financial statements not misleading. Operating results for the three and six months ended June 30, 2024 are not necessarily indicative of the results that may be expected for the year ending December 31, 2024. These condensed financial statements should be read in conjunction with the financial statements and related notes included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2023, as filed with the SEC on March 13, 2024. Reclassifications —Certain immaterial prior year amounts have been reclassified to conform with current year presentation. These reclassifications had no effect on the reported results of operations.

SIGNIFICANT ACCOUNTING POLICIES

SIGNIFICANT ACCOUNTING POLICIES	6 Months Ended
	Jun. 30, 2024
Accounting Policies [Abstract]
SIGNIFICANT ACCOUNTING POLICIES	SIGNIFICANT ACCOUNTING POLICIES The Company’s significant accounting policies have not changed from those disclosed in the annual audited financial statements and accompanying notes in the Annual Report on Form 10-K for the fiscal year ended December 31, 2023. As of July 1, 2023 (the “Transition Date”), the Company transitioned out of the research and development phase and into commercial inventory accounting. As a result of the transition, all inventoriable costs incurred are capitalized, net of any lower of cost or net realizable value (“LCNRV”) charges, which are recognized as cost of revenue. Further, unfulfilled noncancellable purchase commitments are recognized as expense for estimated losses in cost of revenue and warranty and fulfillment costs are recorded as a component of cost of revenue rather than research and development expense beginning on the Transition Date. Refer to the annual audited financial statements and accompanying notes in the Annual Report on Form 10-K for the fiscal year ended December 31, 2023 for further details on the accounting policies resulting from the transition. Recently Issued Accounting Pronouncements - Not Yet Adopted In December 2023, the FASB issued ASU No. 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures . The ASU requires greater disaggregation of income tax disclosures primarily on the income tax rate reconciliation and income taxes paid. This authoritative guidance will be effective for the Company starting in fiscal year ending December 31, 2025, with early adoption permitted. The Company is currently evaluating the effect of this new standard on the Company's disclosures . In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures (“ASU 2023-07”). ASU 2023-07 updates reportable segment disclosure requirements, primarily through enhanced disclosures about significant expenses. ASU 2023-07 requires disclosures to include significant segment expenses that are regularly provided to the chief operating decision maker, a description of other segment items by reportable segment, and any additional measures of a segment's profit or loss used by the chief operating decision maker when deciding how to allocate resources. ASU 2023-07 also requires all annual disclosures currently required by Topic 280 to be included in interim periods. The update is effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024, with early adoption permitted and requires retrospective application to all prior periods presented in the financial statements. The Company is currently evaluating the effect that the adoption of this ASU may have on the Company’s disclosures.

INVENTORY

INVENTORY	6 Months Ended
	Jun. 30, 2024
Inventory Disclosure [Abstract]
INVENTORY	INVENTORY Inventory consists of the following (in thousands): June 30, 2024 December 31, 2023 Raw materials $ 7,796 $ 7,740 Work in process 3,654 1,236 Finished goods 5,035 5,685 Inventory, gross $ 16,485 $ 14,661 Net realizable value adjustment (12,060) (11,295) Inventory $ 4,425 $ 3,366 The balance of the Company’s inventory was written down by $12.1 million and $11.3 million from its cost to its net realizable value as of June 30, 2024 and December 31, 2023, respectively. Additionally, the Company has LCNRV losses related to noncancellable purchase commitments which were $1.4 million and $0.6 million as of June 30, 2024 and December 31, 2023, respectively. These LCNRV losses related to noncancellable purchase commitments are reflected in the materials and related purchases component of accrued and other liabilities on the condensed balance sheets. For further details, refer to Note 8, Commitments and Contingencies .

PROPERTY AND EQUIPMENT, NET

PROPERTY AND EQUIPMENT, NET	6 Months Ended
	Jun. 30, 2024
Property, Plant and Equipment [Abstract]
PROPERTY AND EQUIPMENT, NET	PROPERTY AND EQUIPMENT, NET Property and equipment, net consists of the following (in thousands): June 30, 2024 December 31, 2023 Machinery and equipment $ 19,741 $ 17,669 Furniture and fixtures 231 184 Leasehold improvements 3,236 3,232 Software 183 183 Construction in process 6,037 4,279 Total property and equipment 29,428 25,547 Less accumulated depreciation (11,670) (9,281) Total property and equipment, net $ 17,758 $ 16,266

INTANGIBLE ASSETS, NET

INTANGIBLE ASSETS, NET	6 Months Ended
	Jun. 30, 2024
Goodwill and Intangible Assets Disclosure [Abstract]
INTANGIBLE ASSETS, NET	INTANGIBLE ASSETS, NET In September 2023, the Company acquired patent rights valued at $5.0 million under a Patent License Agreement with UOP LLC (“UOP”), an affiliate of Honeywell International Inc. (“Honeywell”), a related party. These patent rights were recorded at fair value based on the value of the IP Warrants issued, as defined in Note 9, Common Stock Warrants , and are amortized over an average useful life of 19 years based on the remaining useful lives of the patents acquired. Amortization expense for the three and six months ended June 30, 2024 was $67 thousand and $134 thousand, respectively. Intangible assets, net consisted of the following (in thousands): June 30, 2024 December 31, 2023 Cost Accumulated Amortization Net Carrying Amount Cost Accumulated Amortization Net Carrying Amount Patents $ 4,990 $ (200) $ 4,790 $ 4,990 $ (67) $ 4,923

ACCRUED AND OTHER CURRENT LIABI

ACCRUED AND OTHER CURRENT LIABILITIES	6 Months Ended
	Jun. 30, 2024
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): June 30, 2024 December 31, 2023 Payroll and related benefits $ 3,711 $ 5,681 Materials and related purchases 3,234 2,083 Professional and consulting fees 515 802 Amounts due to customers — 545 Accrued capital purchases 283 327 Noncancellable purchase commitments 1,402 637 Other 524 680 Total accrued and other current liabilities $ 9,669 $ 10,755

ACCRUED PRODUCT WARRANTIES

ACCRUED PRODUCT WARRANTIES	6 Months Ended
	Jun. 30, 2024
Guarantees and Product Warranties [Abstract]
ACCRUED PRODUCT WARRANTIES	ACCRUED PRODUCT WARRANTIES The following table summarizes product warranty activity (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Accrued product warranties - beginning of period $ 3,322 $ 2,874 $ 2,129 $ 1,643 Accruals for warranties issued 40 3,674 2,568 5,178 Repairs and replacements (68) (789) (702) (1,062) Adjustments to existing accruals (54) (656) (755) (656) Accrued product warranties - end of period $ 3,240 $ 5,103 $ 3,240 $ 5,103

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	6 Months Ended
	Jun. 30, 2024
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Legal Proceedings 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 material legal proceedings or other claims, legal actions, or complaints through the date of issuance of these condensed financial statements. Letters of Credit The Company has a standby letter of credit with First Republic Bank for $75 thousand as security for an operating lease of office and manufacturing space in Wilsonville, Oregon secured by a restricted certificate of deposit account totaling $75 thousand. As of June 30, 2024 the letter of credit was recorded as restricted cash, non-current. There were no draws against the letter of credit during the three and six months ended June 30, 2024 and 2023. The Company has a standby letter of credit with Bank of America for $600 thousand as security for the performance and payment of the Company’s obligations under a customer agreement. The letter of credit is in effect until the date on which the warranty period under the agreement expires, which is anticipated to be more than a year from the balance sheet date. As of June 30, 2024, $600 thousand was pledged as collateral for the letter of credit and recorded as restricted cash, non-current. There were no draws against the letter of credit during the three and six months ended June 30, 2024 and 2023. The Company has a standby letter of credit with Bank of America for $200 thousand in support of the Company’s customs and duties due on imported materials. The letter of credit is in effect until May 19, 2025. As of June 30, 2024, $200 thousand was pledged as collateral for the letter of credit and recorded as restricted cash, current. There were no draws against the letter of credit during the three and six months ended June 30, 2024 and 2023. Purchase Commitments 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 June 30, 2024 and December 31, 2023, total unfulfilled noncancellable purchase commitments were $1.4 million and $0.6 million, respectively. In addition, total unfulfilled cancellable purchase commitments amounted to $11.8 million and $7.7 million as of June 30, 2024, and December 31, 2023, respectively. Joint Development Agreement In September 2023, the Company entered into a Joint Development Agreement (“JDA”) with UOP, an affiliate of Honeywell, a related party, under which the parties agreed to work collaboratively to engage in certain research and development activities generally related to flow battery technology. Pursuant to the JDA, the Company agreed to reimburse UOP a minimum of $8.0 million for research and development expenses incurred through December 31, 2028. No expenses were incurred under the JDA during the three and six months ended June 30, 2024.

COMMON STOCK WARRANTS

COMMON STOCK WARRANTS	6 Months Ended
	Jun. 30, 2024
Equity [Abstract]
COMMON STOCK WARRANTS	COMMON STOCK WARRANTS Common stock warrant balances consist of the following: June 30, 2024 December 31, 2023 Public Warrants outstanding 11,461,227 11,461,227 SMUD Warrant outstanding 12,500 12,500 Honeywell Warrants outstanding: Investment Warrant outstanding 10,631,633 10,631,633 IP Warrant outstanding 6,269,955 6,269,955 Performance Warrants outstanding 775,760 775,760 Total common stock warrants 29,151,075 29,151,075 As part of STWO’s initial public offering, 8,333,287 warrants to purchase common stock (the “Public Warrants”) were sold. The Public Warrants are listed on the NYSE under the ticker symbol “GWH.W.” 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 expire on October 8, 2026, five years after completion of the Business Combination, or earlier upon redemption or liquidation. The Company may call the Public Warrants for redemption starting any time, in whole and not in part, at a price of $0.01 per warrant, so long as the Company provides no 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 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 any time, in whole and not in part, at a price of $0.10 per warrant, so long as the Company provides no 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 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 issued in a private placement 4,666,667 warrants to purchase common stock (the “Private Warrants”) to 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. The Private Warrants, including the Earnout Warrants, automatically converted on a 1:1 basis into Public Warrants upon the transfer of such warrants by the initial holder to a third party during the fourth quarter of 2023. The table below shows the common stock warrant activities during the six months ended June 30, 2024: December 31, 2023 Issued Exercised June 30, 2024 Public Warrants 11,461,227 — — 11,461,227 SMUD Warrant 12,500 — — 12,500 Investment Warrant 10,631,633 — — 10,631,633 IP Warrant 6,269,955 — — 6,269,955 Performance Warrants 775,760 — — 775,760 Total common stock warrants 29,151,075 — — 29,151,075 The table below shows the common stock warrant activities during the six months ended June 30, 2023: December 31, 2022 Issued Exercised June 30, 2023 Earnout Warrants 583,334 — — 583,334 Public Warrants 7,377,893 — — 7,377,893 Private Warrants (excluding Earnout Warrants) 3,500,000 — — 3,500,000 SMUD Warrant 12,500 — — 12,500 Total common stock warrants 11,473,727 — — 11,473,727 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 in the condensed statements of operations and comprehensive loss. For the three and six months ending June 30, 2024, the Company recorded a net decrease to the liabilities for Public Warrants of $0.1 million and $0.1 million, respectively. For the three and six months ended June 30, 2023, the Company recorded a net increase and net decrease to the liabilities for Earnout Warrants, Public Warrants and Private Warrants (excluding Earnout Warrants) of $0.1 million and $0.6 million, respectively. SMUD Warrant On September 16, 2022, the Company entered into a warrant agreement with the Sacramento Municipal Utility District (“SMUD”), whereby the Company agreed to issue a warrant for up to 500,000 shares of the Company’s common stock at an exercise price of $4.296 per share. The vesting of the shares underlying the warrant will be subject to the achievement of certain commercial milestones through December 31, 2030 pursuant to a related commercial agreement. As of June 30, 2024 and December 31, 2023, 12,500 shares underlying the warrant were vested. Honeywell Warrants On September 21, 2023, the Company entered into a Common Stock and Warrant Purchase Agreement (the “Purchase Agreement”) with Honeywell ACS Ventures LLC (“Honeywell Ventures”), an affiliate of Honeywell, a related party. Pursuant to the Purchase Agreement, Honeywell invested $27.5 million in the Company and the Company issued 16,491,754 shares of common stock and a warrant to issue up to 10,631,633 shares of common stock (the “Investment Warrant”) to Honeywell Ventures. Pursuant to the Purchase Agreement and also as further consideration for the licensing by UOP, an affiliate of Honeywell, of certain intellectual property to the Company, the Company issued a warrant to issue up to 6,269,955 shares of common stock (the “IP Warrant”) to UOP. The Investment Warrant has an exercise price of $1.89, and the IP Warrant has an exercise price of $2.90. Each warrant will expire on September 21, 2028. On September 21, 2023, the Company and UOP also entered into a Master Supply Agreement (the “Supply Agreement”), pursuant to which UOP may purchase equipment supplied by the Company. Pursuant to the Supply Agreement, the Company agreed to issue additional warrants to purchase common stock to UOP, consisting of (i) an initial performance warrant to issue up to 775,760 shares of common stock, issued on September 21, 2023 in exchange for a prepayment of equipment by UOP in the amount of $15 million, and (ii) additional performance warrants (not to exceed an aggregate value of $15 million based on target purchase amounts of up to $300 million by 2030) to be issued on an annual basis for the five-year period beginning in 2026, based on UOP’s purchase of additional equipment after execution of the Supply Agreement (the “Performance Warrants”). The initial Performance Warrant has an exercise price of $1.45 and the additional Performance Warrants will have an exercise price equal to the volume-weighted average price of the Company’s common stock for the last fifteen (15) trading days of the relevant calendar year for which such Performance Warrant is being issued. The initial Performance Warrant will expire on September 21, 2028 and each additional Performance Warrant will have a five-year term from its respective date of issuance.

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	6 Months Ended
	Jun. 30, 2024
Share-Based Payment Arrangement [Abstract]
STOCK-BASED COMPENSATION	STOCK-BASED COMPENSATION 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 issued to employees on the Company’s condensed statements of operations and comprehensive loss (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Cost of revenue $ 415 $ — $ 1,339 $ — Research and development 908 1,130 1,309 2,123 Sales and marketing 163 165 258 315 General and administrative 1,540 1,430 2,974 2,346 Total stock-based compensation $ 3,026 $ 2,725 $ 5,880 $ 4,784 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. Stock awards under the plan may be issued as Incentive Stock Options (“ISO”), Non-statutory Stock Options (“NSO”), Stock Appreciation Rights, and Restricted Stock Awards (“RSU”). Only employees are eligible to receive ISO awards. Employees, directors, and consultants who provide 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. As of January 1, 2024, the number of shares available for issuance under the 2021 Plan was increased by 8,700,000 shares in accordance with the plan and as approved by the Board. Under the 2021 Plan, the Company is authorized to issue 26,310,000 shares of common stock as of June 30, 2024. Option prices for incentive stock options are set at the fair market value of the Company’s common stock at the date of grant. The fair market value of RSUs is set at the closing sales price of the Company’s common stock at the date of grant. Employee new hire grants generally cliff vest 1/4 th at the end of the first year and then vest 1/16 th each quarter over the remaining three years. Grants expire 10 years from the date of grant. All other grants vest quarterly over four years. As of June 30, 2024, there were 5,376,809 shares available for future grant under the 2021 Plan. Stock Options and Restricted Stock Units Stock option and RSU activity, prices, and values during the six months ended June 30, 2024 are 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, 2023 2,598,382 $ 1.33 6.25 $ 1,422 13,162,368 $ 2.79 Options and RSUs granted — — 11,851,132 0.94 Options exercised and RSUs released (48,867) 0.44 (2,579,523) 2.09 Options and RSUs forfeited (10,972) 0.54 (2,661,399) 1.85 Balances as of June 30, 2024 2,538,543 $ 1.35 6.37 $ 807 19,772,578 $ 1.90 Options vested and exercisable - December 31, 2023 1,775,256 $ 1.10 5.62 $ 1,198 Options vested and exercisable - June 30, 2024 1,936,099 $ 1.17 5.78 $ 756 No options were granted during the three and six months ended June 30, 2024 and 2023. As of June 30, 2024, there was approximately $26.0 million of unamortized stock-based compensation expense related to unvested stock options and RSUs, which is expected to be recognized over a weighted-average period of 2.86 years. Employee Stock Purchase Plan In May 2022, the Company commenced its first offering period under the ESS Tech, Inc. Employee Stock Purchase Plan (“ESPP”), which assists employees in acquiring a stock ownership interest in the Company. The ESPP permits eligible employees to purchase common stock at a discount through payroll deductions during specified offering periods. No employee may purchase more than $25,000 worth of stock in any calendar year. The price of shares purchased under the ESPP is equal to 85% of the fair market value of the common stock on the first or last day of the offering period, whichever is lower. Total ESPP expense for the three and six months ended June 30, 2024 and 2023 was $65 thousand and $149 thousand and $90 thousand and $149 thousand, respectively.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	6 Months Ended
	Jun. 30, 2024
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS The following tables present the Company’s fair value hierarchy for its financial assets measured at fair value on a recurring basis (in thousands): June 30, 2024 Cash Equivalents and Restricted Cash Short-Term Investments Total Assets at Fair Value Level 1: Money market funds $ 10,200 $ — $ 10,200 U.S. Treasury securities 22,569 21,132 43,701 Total Level 1 32,769 21,132 53,901 Level 2: Certificate of deposit 77 — 77 Commercial paper 3,458 16,563 20,021 Total Level 2 3,535 16,563 20,098 Total assets measured at fair value $ 36,304 $ 37,695 $ 73,999 December 31, 2023 Cash Equivalents and Restricted Cash Short-Term Investments Total Assets at Fair Value Level 1: Money market funds $ 10,126 $ — $ 10,126 U.S. Treasury securities — 54,681 54,681 Total Level 1 10,126 54,681 64,807 Level 2: Certificate of deposit 77 — 77 U.S. agency securities — 12,447 12,447 Commercial paper 9,353 20,771 30,124 Total Level 2 9,430 33,218 42,648 Total assets measured at fair value $ 19,556 $ 87,899 $ 107,455 The following tables present the Company’s fair value hierarchy for its financial liabilities measured at fair value on a recurring basis (in thousands): June 30, 2024 Level 1 Level 2 Level 3 Total Liabilities: Public common stock warrants 802 — — 802 Total liabilities measured at fair value $ 802 $ — $ — $ 802 December 31, 2023 Level 1 Level 2 Level 3 Total Liabilities: Public common stock warrants 917 — — 917 Total liabilities measured at fair value $ 917 $ — $ — $ 917 There were no transfers among Level 1, Level 2, or Level 3 categories during the periods presented. The carrying amounts of the Company’s accounts payable approximate their fair values due to their short maturities. Level 1 Assets: The Company invests in money market funds and U.S. Treasury securities. These assets are valued using observable inputs that reflect quoted prices for securities with identical characteristics. Level 2 Assets: The Company invests in a certificate of deposit, U.S. agency securities, and commercial paper. These assets are valued using observable inputs that reflect quoted prices for securities with similar characteristics and other observable inputs (such as interest rates that are observable at commonly quoted intervals). Level 1 Liabilities: The Company values its public common stock warrants based on the market price of the warrants.

INCOME TAXES

INCOME TAXES	6 Months Ended
	Jun. 30, 2024
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES

GOVERNMENT GRANTS

GOVERNMENT GRANTS	6 Months Ended
	Jun. 30, 2024
Government Assistance [Abstract]
GOVERNMENT GRANTS	GOVERNMENT GRANTS Inflation Reduction Act of 2022 (“IRA”) On August 16, 2022, President Biden signed the Inflation Reduction Act of 2022 into law. The IRA has significant economic incentives for both energy storage customers and manufacturers for projects placed in service after December 31, 2022. Starting in 2023, there are Production Tax Credits under Internal Revenue Code 45X (“PTC”), that can be claimed on battery components manufactured in the U.S. and sold to U.S. or foreign customers. The tax credits available to manufacturers include a credit for ten percent of the cost incurred to make electrode active materials in addition to credits of $35 per kWh of capacity of battery cells and $10 per kWh of capacity of battery modules. The credits are cumulative, meaning that companies will be able to claim each of the available tax credits based on the battery components produced and sold through 2029, after which the PTC will begin to gradually phase down through 2032. Since the PTC is a refundable credit (i.e., a credit with a direct-pay option available), the PTC is outside the scope of ASC 740, Income Taxes (“ASC 740”). Therefore, the Company accounts for the PTC under a government grant model. GAAP does not address the accounting for government grants received by a business entity that are outside the scope of ASC 740. The Company’s accounting policy is to analogize to IAS 20, Accounting for Government Grants and Disclosure of Government Assistance , under IFRS Accounting Standards. Under IAS 20, once it is reasonably assured that the entity will comply with the conditions of the grant, the grant money should be recognized on a systematic basis over the periods in which the entity recognizes the related expenses or losses for which the grant money is intended to compensate. The Company recognizes grants once it is probable that both of the following conditions will be met: (1) the Company is eligible to receive the grant and (2) the Company is able to comply with the relevant conditions of the grant. The PTC is recorded as the applicable items are produced and sold. The Company began earning PTCs in the third quarter of 2023. For the three and six months ended June 30, 2024, the Company recognized PTC of $54 thousand and $284 thousand, respectively, as a reduction of cost of revenue on the condensed statements of operations and comprehensive loss. As of June 30, 2024 and December 31, 2023, grant receivable related to the PTC in the amount of $1.1 million and $0.8 million is recorded in prepaid expenses and other current assets

REVENUE

REVENUE	6 Months Ended
	Jun. 30, 2024
Revenue from Contract with Customer [Abstract]
REVENUE	REVENUE Disaggregated Revenue The following table presents the Company’s revenue, disaggregated by source (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Product revenue $ 196 $ 2,822 $ 2,828 $ 3,188 Service revenue 61 5 78 11 Other revenue 91 — 180 — Total revenue $ 348 $ 2,827 $ 3,086 $ 3,199 The majority of the Company’s revenue is derived from product sales of energy storage systems. During 2024 other revenue included engineering services the Company performed in support of a customer project site and customer reimbursements for freight, travel, and other expenses. Contract Balances Contract assets relate to unbilled amounts resulting from contract arrangements in which the related revenue recognition performance obligations have been satisfied, however invoicing to the customer has not yet occurred. Deferred revenue (or contract liabilities) relates to consideration received from customers in advance of the Company satisfying the revenue recognition performance obligations under the related contractual arrangements. Contract balances are reported in a net contract asset or deferred revenue liability position on a contract-by-contract basis at the end of each reporting period. Contract assets are included in prepaid expenses and other current assets and deferred revenue is presented separately on the condensed balance sheets. The following table provides information about contract assets and deferred revenue from contracts with customers (in thousands): June 30, 2024 December 31, 2023 Contract assets $ 126 $ 253 Deferred revenue 20,089 20,781 Contract assets decreased by $127 thousand during the six months ended June 30, 2024 due to invoicing on contracts for which revenue has previously been recognized. Deferred revenue decreased by $0.7 million during the six months ended June 30, 2024 reflecting $0.2 million in customer advance payments offset by the recognition of $0.9 million of revenue that was included in the deferred revenue balance at the beginning of the period. Deferred revenue of $5.7 million is expected to be recognized within the next 12 months and non-current deferred revenue of $14.4 million is expected to be recognized thereafter.

RELATED PARTY TRANSACTIONS

RELATED PARTY TRANSACTIONS	6 Months Ended
	Jun. 30, 2024
Related Party Transactions [Abstract]
RELATED PARTY TRANSACTIONS	RELATED PARTY TRANSACTIONS During the three and six months ended June 30, 2024, the Company recognized revenue of $6 thousand and $0.5 million, respectively, for reimbursable expenses, sale of energy storage systems, and extended warranty services provided to related parties. During the three and six months ended June 30, 2023, the Company recognized revenue of $1 thousand and $2 thousand, respectively, for extended warranty services provided to related parties. As of June 30, 2024, the Company had $27 thousand of deferred revenue for extended warranty services to related parties and $87 thousand of accounts receivable for reimbursable expenses and extended warranty services from related parties. As of December 31, 2023, the Company had recorded deferred revenue of $1 thousand for extended warranty services provided to related parties and $29 thousand of outstanding accounts receivable from related parties. As of June 30, 2024 and December 31, 2023, the Company recorded a non-refundable deposit for future equipment purchases by Honeywell of $14.4 million within non-current deferred revenue. As of December 31, 2023, the Company recorded $0.6 million in current deferred revenue which was subsequently recognized as revenue during the six months ended June 30, 2024. As of June 30, 2024 and December 31, 2023, the value of the initial Performance Warrant issued to Honeywell was $0.7 million included within other non-current assets in the condensed balance sheets. During the six months ended June 30, 2024, $27 thousand of the value of the initial Performance Warrant was amortized as an offset to the revenue recognized in the period.

NET LOSS PER SHARE

NET LOSS PER SHARE	6 Months Ended
	Jun. 30, 2024
Earnings Per Share [Abstract]
NET LOSS PER SHARE	NET LOSS PER SHARE The following table presents the calculation of basic and diluted net loss per share attributable to common stockholders (in thousands, except share and per share data): Three Months Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Numerator: Net loss attributable to common stockholders $ (21,940) $ (22,929) $ (40,250) $ (44,830) Denominator: Weighted-average shares outstanding – basic and diluted 175,758,584 154,900,330 175,136,561 154,514,265 Net loss per share – basic and diluted $ (0.12) $ (0.15) $ (0.23) $ (0.29) Due to the net losses for the three and six months ended June 30, 2024 and 2023, 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 equivalents have been excluded from the calculation of diluted weighted-average common shares outstanding because the effect is anti-dilutive for the periods presented: Three and Six Months Ended June 30, 2024 2023 Stock options 2,538,543 2,575,206 RSUs 19,772,578 12,613,177 Warrants 29,151,075 11,473,727 Total 51,462,196 26,662,110

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	6 Months Ended
	Jun. 30, 2024
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTS On July 12, 2024, the board of directors of the Company voted unanimously to approve and to recommend to the Company’s stockholders that they approve at a special meeting of the Company’s stockholders to be held on August 23, 2024, six possible amendments of our certificate of incorporation (the “Certificate”) to effect a reverse stock split of the Company’s common stock issued and outstanding or held in treasury at a ratio of 1-for-8, 1-for-10, 1-for-12, 1-for-15, 1-for-20, or 1-for-25 (the “Reverse Stock Split”) and, in the case of each such amendment, contemporaneously with the Reverse Stock Split, a reduction to the number of shares of authorized common stock from 2,000,000,000 to 1,000,000,000 (the “Authorized Share Reduction”). If approved by the stockholders at the special meeting, at the discretion of the board of directors, the Company may effect the Reverse Stock Split and the Authorized Share Reduction by causing the filing of one of six possible amendments to the Certificate (each, a “Reverse Stock Split Amendment” and collectively, the “Reverse Stock Split Amendments”), with the Delaware Secretary of State. The par value per share of the Company’s common stock would remain unchanged at $0.0001. The Reverse Stock Split would be primarily intended to bring the Company into compliance with the continued listing standards of the New York Stock Exchange. The financial statements contained herein do not reflect the Reverse Stock Split as the Reverse Stock Split has not been approved by the Company’s stockholders and has not become effective as of the date of the issuance of these financial statements.

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2024	Jun. 30, 2023
Pay vs Performance Disclosure
Net loss	$ (21,940)	$ (18,310)	$ (22,929)	$ (21,901)	$ (40,250)	$ (44,830)

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Jun. 30, 2024
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

SIGNIFICANT ACCOUNTING POLICI_2

SIGNIFICANT ACCOUNTING POLICIES (Policies)	6 Months Ended
	Jun. 30, 2024
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation —The accompanying condensed financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”).
Reclassifications	Reclassifications —Certain immaterial prior year amounts have been reclassified to conform with current year presentation. These reclassifications had no effect on the reported results of operations.
Recently Issued Accounting Pronouncements - Not Yet Adopted	Recently Issued Accounting Pronouncements - Not Yet Adopted In December 2023, the FASB issued ASU No. 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures . The ASU requires greater disaggregation of income tax disclosures primarily on the income tax rate reconciliation and income taxes paid. This authoritative guidance will be effective for the Company starting in fiscal year ending December 31, 2025, with early adoption permitted. The Company is currently evaluating the effect of this new standard on the Company's disclosures . In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures (“ASU 2023-07”). ASU 2023-07 updates reportable segment disclosure requirements, primarily through enhanced disclosures about significant expenses. ASU 2023-07 requires disclosures to include significant

INVENTORY (Tables)

INVENTORY (Tables)	6 Months Ended
	Jun. 30, 2024
Inventory Disclosure [Abstract]
Schedule of Inventory	Inventory consists of the following (in thousands): June 30, 2024 December 31, 2023 Raw materials $ 7,796 $ 7,740 Work in process 3,654 1,236 Finished goods 5,035 5,685 Inventory, gross $ 16,485 $ 14,661 Net realizable value adjustment (12,060) (11,295) Inventory $ 4,425 $ 3,366

PROPERTY AND EQUIPMENT, NET (Ta

PROPERTY AND EQUIPMENT, NET (Tables)	6 Months Ended
	Jun. 30, 2024
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net consists of the following (in thousands): June 30, 2024 December 31, 2023 Machinery and equipment $ 19,741 $ 17,669 Furniture and fixtures 231 184 Leasehold improvements 3,236 3,232 Software 183 183 Construction in process 6,037 4,279 Total property and equipment 29,428 25,547 Less accumulated depreciation (11,670) (9,281) Total property and equipment, net $ 17,758 $ 16,266

INTANGIBLE ASSETS, NET (Tables)

INTANGIBLE ASSETS, NET (Tables)	6 Months Ended
	Jun. 30, 2024
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Intangible Assets, Net	Intangible assets, net consisted of the following (in thousands): June 30, 2024 December 31, 2023 Cost Accumulated Amortization Net Carrying Amount Cost Accumulated Amortization Net Carrying Amount Patents $ 4,990 $ (200) $ 4,790 $ 4,990 $ (67) $ 4,923

ACCRUED AND OTHER CURRENT LIA_2

ACCRUED AND OTHER CURRENT LIABILITIES (Tables)	6 Months Ended
	Jun. 30, 2024
Payables and Accruals [Abstract]
Schedule of Accrued and Other Current Liabilities	Accrued and other current liabilities consist of the following (in thousands): June 30, 2024 December 31, 2023 Payroll and related benefits $ 3,711 $ 5,681 Materials and related purchases 3,234 2,083 Professional and consulting fees 515 802 Amounts due to customers — 545 Accrued capital purchases 283 327 Noncancellable purchase commitments 1,402 637 Other 524 680 Total accrued and other current liabilities $ 9,669 $ 10,755

ACCRUED PRODUCT WARRANTIES (Tab

ACCRUED PRODUCT WARRANTIES (Tables)	6 Months Ended
	Jun. 30, 2024
Guarantees and Product Warranties [Abstract]
Schedule of Product Warranty Activity	The following table summarizes product warranty activity (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Accrued product warranties - beginning of period $ 3,322 $ 2,874 $ 2,129 $ 1,643 Accruals for warranties issued 40 3,674 2,568 5,178 Repairs and replacements (68) (789) (702) (1,062) Adjustments to existing accruals (54) (656) (755) (656) Accrued product warranties - end of period $ 3,240 $ 5,103 $ 3,240 $ 5,103

COMMON STOCK WARRANTS (Tables)

COMMON STOCK WARRANTS (Tables)	6 Months Ended
	Jun. 30, 2024
Equity [Abstract]
Schedule of Common Stock Warrant Activity	Common stock warrant balances consist of the following: June 30, 2024 December 31, 2023 Public Warrants outstanding 11,461,227 11,461,227 SMUD Warrant outstanding 12,500 12,500 Honeywell Warrants outstanding: Investment Warrant outstanding 10,631,633 10,631,633 IP Warrant outstanding 6,269,955 6,269,955 Performance Warrants outstanding 775,760 775,760 Total common stock warrants 29,151,075 29,151,075 The table below shows the common stock warrant activities during the six months ended June 30, 2024: December 31, 2023 Issued Exercised June 30, 2024 Public Warrants 11,461,227 — — 11,461,227 SMUD Warrant 12,500 — — 12,500 Investment Warrant 10,631,633 — — 10,631,633 IP Warrant 6,269,955 — — 6,269,955 Performance Warrants 775,760 — — 775,760 Total common stock warrants 29,151,075 — — 29,151,075 The table below shows the common stock warrant activities during the six months ended June 30, 2023: December 31, 2022 Issued Exercised June 30, 2023 Earnout Warrants 583,334 — — 583,334 Public Warrants 7,377,893 — — 7,377,893 Private Warrants (excluding Earnout Warrants) 3,500,000 — — 3,500,000 SMUD Warrant 12,500 — — 12,500 Total common stock warrants 11,473,727 — — 11,473,727

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	6 Months Ended
	Jun. 30, 2024
Share-Based Payment Arrangement [Abstract]
Schedule of Stock-Based Compensation	The following table presents the amount of stock-based compensation related to stock-based awards issued to employees on the Company’s condensed statements of operations and comprehensive loss (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Cost of revenue $ 415 $ — $ 1,339 $ — Research and development 908 1,130 1,309 2,123 Sales and marketing 163 165 258 315 General and administrative 1,540 1,430 2,974 2,346 Total stock-based compensation $ 3,026 $ 2,725 $ 5,880 $ 4,784
Schedule of Stock Options Activity	Stock option and RSU activity, prices, and values during the six months ended June 30, 2024 are 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, 2023 2,598,382 $ 1.33 6.25 $ 1,422 13,162,368 $ 2.79 Options and RSUs granted — — 11,851,132 0.94 Options exercised and RSUs released (48,867) 0.44 (2,579,523) 2.09 Options and RSUs forfeited (10,972) 0.54 (2,661,399) 1.85 Balances as of June 30, 2024 2,538,543 $ 1.35 6.37 $ 807 19,772,578 $ 1.90 Options vested and exercisable - December 31, 2023 1,775,256 $ 1.10 5.62 $ 1,198 Options vested and exercisable - June 30, 2024 1,936,099 $ 1.17 5.78 $ 756
Schedule of Restricted Stock Units Activity	Stock option and RSU activity, prices, and values during the six months ended June 30, 2024 are 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, 2023 2,598,382 $ 1.33 6.25 $ 1,422 13,162,368 $ 2.79 Options and RSUs granted — — 11,851,132 0.94 Options exercised and RSUs released (48,867) 0.44 (2,579,523) 2.09 Options and RSUs forfeited (10,972) 0.54 (2,661,399) 1.85 Balances as of June 30, 2024 2,538,543 $ 1.35 6.37 $ 807 19,772,578 $ 1.90 Options vested and exercisable - December 31, 2023 1,775,256 $ 1.10 5.62 $ 1,198 Options vested and exercisable - June 30, 2024 1,936,099 $ 1.17 5.78 $ 756

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	6 Months Ended
	Jun. 30, 2024
Fair Value Disclosures [Abstract]
Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis	The following tables present the Company’s fair value hierarchy for its financial assets measured at fair value on a recurring basis (in thousands): June 30, 2024 Cash Equivalents and Restricted Cash Short-Term Investments Total Assets at Fair Value Level 1: Money market funds $ 10,200 $ — $ 10,200 U.S. Treasury securities 22,569 21,132 43,701 Total Level 1 32,769 21,132 53,901 Level 2: Certificate of deposit 77 — 77 Commercial paper 3,458 16,563 20,021 Total Level 2 3,535 16,563 20,098 Total assets measured at fair value $ 36,304 $ 37,695 $ 73,999 December 31, 2023 Cash Equivalents and Restricted Cash Short-Term Investments Total Assets at Fair Value Level 1: Money market funds $ 10,126 $ — $ 10,126 U.S. Treasury securities — 54,681 54,681 Total Level 1 10,126 54,681 64,807 Level 2: Certificate of deposit 77 — 77 U.S. agency securities — 12,447 12,447 Commercial paper 9,353 20,771 30,124 Total Level 2 9,430 33,218 42,648 Total assets measured at fair value $ 19,556 $ 87,899 $ 107,455 The following tables present the Company’s fair value hierarchy for its financial liabilities measured at fair value on a recurring basis (in thousands): June 30, 2024 Level 1 Level 2 Level 3 Total Liabilities: Public common stock warrants 802 — — 802 Total liabilities measured at fair value $ 802 $ — $ — $ 802 December 31, 2023 Level 1 Level 2 Level 3 Total Liabilities: Public common stock warrants 917 — — 917 Total liabilities measured at fair value $ 917 $ — $ — $ 917

REVENUE (Tables)

REVENUE (Tables)	6 Months Ended
	Jun. 30, 2024
Revenue from Contract with Customer [Abstract]
Schedule of Revenue Disaggregated by Source	The following table presents the Company’s revenue, disaggregated by source (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Product revenue $ 196 $ 2,822 $ 2,828 $ 3,188 Service revenue 61 5 78 11 Other revenue 91 — 180 — Total revenue $ 348 $ 2,827 $ 3,086 $ 3,199
Schedule of Contract Asset and Deferred Revenue	The following table provides information about contract assets and deferred revenue from contracts with customers (in thousands): June 30, 2024 December 31, 2023 Contract assets $ 126 $ 253 Deferred revenue 20,089 20,781

NET LOSS PER SHARE (Tables)

NET LOSS PER SHARE (Tables)	6 Months Ended
	Jun. 30, 2024
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 share and per share data): Three Months Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Numerator: Net loss attributable to common stockholders $ (21,940) $ (22,929) $ (40,250) $ (44,830) Denominator: Weighted-average shares outstanding – basic and diluted 175,758,584 154,900,330 175,136,561 154,514,265 Net loss per share – basic and diluted $ (0.12) $ (0.15) $ (0.23) $ (0.29)
Schedule of Securities Excluded from Calculation of Diluted Weighted-Average Common Shares Outstanding	The following outstanding balances of common share equivalents have been excluded from the calculation of diluted weighted-average common shares outstanding because the effect is anti-dilutive for the periods presented: Three and Six Months Ended June 30, 2024 2023 Stock options 2,538,543 2,575,206 RSUs 19,772,578 12,613,177 Warrants 29,151,075 11,473,727 Total 51,462,196 26,662,110

DESCRITPION OF BUSINESS AND B_2

DESCRITPION OF BUSINESS AND BASIS OF PRESENTATION (Details)	6 Months Ended
	Jun. 30, 2024 h
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Battery, flexible energy capacity, minimum	4

INVENTORY - Schedule of Invento

INVENTORY - Schedule of Inventory (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Inventory Disclosure [Abstract]
Raw materials	$ 7,796	$ 7,740
Work in process	3,654	1,236
Finished goods	5,035	5,685
Inventory, gross	16,485	14,661
Net realizable value adjustment	(12,060)	(11,295)
Inventory	$ 4,425	$ 3,366

INVENTORY - Narrative (Details)

INVENTORY - Narrative (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Inventory [Line Items]
Net realizable value adjustment	$ 12,060	$ 11,295
Noncancellable Agreement
Inventory [Line Items]
Purchase commitments	$ 1,400	$ 600

PROPERTY AND EQUIPMENT, NET (De

PROPERTY AND EQUIPMENT, NET (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 29,428		$ 29,428		$ 25,547
Less accumulated depreciation	(11,670)		(11,670)		(9,281)
Total property and equipment, net	17,758		17,758		16,266
Depreciation expense	1,200	$ 1,000	2,400	$ 2,100
Machinery and equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	19,741		19,741		17,669
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property and equipment	231		231		184
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment	3,236		3,236		3,232
Software
Property, Plant and Equipment [Line Items]
Total property and equipment	183		183		183
Construction in process
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 6,037		$ 6,037		$ 4,279

INTANGIBLE ASSETS, NET - Narrat

INTANGIBLE ASSETS, NET - Narrative (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	6 Months Ended
	Sep. 30, 2023	Jun. 30, 2024	Jun. 30, 2024
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization of Intangible Assets		$ 67	$ 134
Patents
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 5,000
Intangible asset, useful life (in years)		19 years	19 years

INTANGIBLE ASSETS, NET - Schedu

INTANGIBLE ASSETS, NET - Schedule of Intangible Assets, Net (Details) - Patents - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Finite-Lived Intangible Assets [Line Items]
Cost	$ 4,990	$ 4,990
Accumulated Amortization	(200)	(67)
Net Carrying Amount	$ 4,790	$ 4,923

ACCRUED AND OTHER CURRENT LIA_3

ACCRUED AND OTHER CURRENT LIABILITIES (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Payables and Accruals [Abstract]
Payroll and related benefits	$ 3,711	$ 5,681
Materials and related purchases	3,234	2,083
Professional and consulting fees	515	802
Amounts due to customers	0	545
Accrued capital purchases	283	327
Noncancellable purchase commitments	1,402	637
Other	524	680
Total accrued and other current liabilities	$ 9,669	$ 10,755

ACCRUED PRODUCT WARRANTIES (Det

ACCRUED PRODUCT WARRANTIES (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Movement in Standard Product Warranty Accrual [Roll Forward]
Product warranties at beginning of period	$ 3,322	$ 2,874	$ 2,129	$ 1,643
Accruals for warranties issued	40	3,674	2,568	5,178
Repairs and replacements	(68)	(789)	(702)	(1,062)
Adjustments to existing accruals	(54)	(656)	(755)	(656)
Product warranties at end of period	$ 3,240	$ 5,103	$ 3,240	$ 5,103

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Details) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Sep. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Other Commitments [Line Items]
Restricted certificate of deposit		$ 75,000		$ 75,000
Research and development		2,836,000	$ 19,450,000	6,382,000	$ 37,181,000
Joint Development Agreement | UOP
Other Commitments [Line Items]
Research and development	$ 8,000,000	0		0
Noncancellable Agreement
Other Commitments [Line Items]
Purchase commitments		1,400,000		1,400,000		$ 600,000
Cancellable Agreement
Other Commitments [Line Items]
Purchase commitments		11,800,000		11,800,000		7,700,000
Letter of Credit | First Republic Bank
Other Commitments [Line Items]
Standby letter of credit						75,000
Draws against letter of credit		0	0	0	0
Letter of Credit | CitiBank N.A
Other Commitments [Line Items]
Standby letter of credit						600,000
Draws against letter of credit		0	0	0	0
Letter of Credit | CitiBank N.A | Asset Pledged as Collateral
Other Commitments [Line Items]
Amounts pledged as collateral		600,000		600,000
Letter of Credit | First Citizens BancShares
Other Commitments [Line Items]
Standby letter of credit						$ 200,000
Draws against letter of credit		0	$ 0	0	$ 0
Letter of Credit | First Citizens BancShares | Asset Pledged as Collateral
Other Commitments [Line Items]
Amounts pledged as collateral		$ 200,000		$ 200,000

COMMON STOCK WARRANTS - Schedul

COMMON STOCK WARRANTS - Schedule of Common Stock Warrant Balances (Details) - shares	Jun. 30, 2024	Dec. 31, 2023	Jun. 30, 2023	Dec. 31, 2022
Class of Warrant or Right [Line Items]
Warrants (in shares)	29,151,075	29,151,075	11,473,727	11,473,727
Public Warrants outstanding
Class of Warrant or Right [Line Items]
Warrants (in shares)	11,461,227	11,461,227	7,377,893	7,377,893
SMUD Warrant outstanding
Class of Warrant or Right [Line Items]
Warrants (in shares)	12,500	12,500	12,500	12,500
Investment Warrant outstanding
Class of Warrant or Right [Line Items]
Warrants (in shares)	10,631,633	10,631,633
IP Warrant outstanding
Class of Warrant or Right [Line Items]
Warrants (in shares)	6,269,955	6,269,955
Performance Warrants outstanding
Class of Warrant or Right [Line Items]
Warrants (in shares)	775,760	775,760

COMMON STOCK WARRANTS - Narrati

COMMON STOCK WARRANTS - Narrative (Details) $ / shares in Units, $ in Thousands				3 Months Ended		6 Months Ended
	Sep. 21, 2023 USD ($) tradingDay $ / shares shares	Oct. 08, 2021 $ / shares shares	Sep. 21, 2020 shares	Jun. 30, 2024 USD ($) $ / shares shares	Jun. 30, 2023 USD ($) shares	Jun. 30, 2024 USD ($) $ / shares shares	Jun. 30, 2023 USD ($) shares	Dec. 31, 2023 shares	Dec. 31, 2022 shares	Sep. 16, 2022 $ / shares shares	Nov. 09, 2021 shares
Class of Warrant or Right [Line Items]
Warrants issued (in shares)						0	0
Warrants (in shares)				29,151,075	11,473,727	29,151,075	11,473,727	29,151,075	11,473,727
Conversion ratio											1
Net decrease to warrant liabilities | $				$ 115	$ (115)	$ 115	$ 573
Number of shares with vesting conditions met (in shares)				12,500		12,500		12,500
Scenario two
Class of Warrant or Right [Line Items]
Price of common stock triggering redemption of warrants (in USD per share) | $ / shares						$ 10
Trading days triggering redemption of warrants						20 days
Consecutive trading day period						30 days
STWO | Common Stock
Class of Warrant or Right [Line Items]
Price per share (in USD per share) | $ / shares		$ 11.50
STWO | Private Warrants | ACON S2 Acquisition Corp. Sponsor | Private Placement
Class of Warrant or Right [Line Items]
Shares issued (in shares)			4,666,667
STWO | Public Warrant Holders | Common Stock
Class of Warrant or Right [Line Items]
Issuance of shares (in shares)		1
Public common stock warrants
Class of Warrant or Right [Line Items]
Warrants issued (in shares)						0	0
Warrants (in shares)				11,461,227	7,377,893	11,461,227	7,377,893	11,461,227	7,377,893
Net decrease to warrant liabilities | $				$ 100	$ (100)	$ 100	$ 600
Public common stock warrants | Scenario one
Class of Warrant or Right [Line Items]
Redemption price per share (in USD per share) | $ / shares				$ 0.01		$ 0.01
Price of common stock triggering redemption of warrants (in USD per share) | $ / shares						$ 18
Trading days triggering redemption of warrants						20 days
Consecutive trading day period						30 days
Public common stock warrants | Scenario two
Class of Warrant or Right [Line Items]
Redemption price per share (in USD per share) | $ / shares				$ 0.10		$ 0.10
Public common stock warrants | STWO
Class of Warrant or Right [Line Items]
Warrants issued (in shares)		8,333,287
Warrants term (in years)		5 years
Private Warrants
Class of Warrant or Right [Line Items]
Warrants issued (in shares)							0
Warrants (in shares)		4,083,334			3,500,000		3,500,000		3,500,000
Warrants vested (in shares)		3,500,000
Private Warrants | ACON S2 Acquisition Corp. Sponsor
Class of Warrant or Right [Line Items]
Warrants forfeited (in shares)		583,333
Earnout Warrants
Class of Warrant or Right [Line Items]
Warrants issued (in shares)							0
Warrants (in shares)					583,334		583,334		583,334
Warrants vested (in shares)											583,334
SMUD Warrant outstanding
Class of Warrant or Right [Line Items]
Warrants issued (in shares)						0	0
Warrants (in shares)				12,500	12,500	12,500	12,500	12,500	12,500
Class of warrant or right, number of securities called by each warrant or right (in shares)										500,000
Class of warrant or right, exercise price of warrants or rights (in dollars per share) | $ / shares										$ 4.296
Honeywell Warrants
Class of Warrant or Right [Line Items]
Shares issued (in shares)	16,491,754
Proceeds from issuance of common stock and common stock warrants, net of issuance costs | $	$ 27,500
Honeywell Warrants | IP Warrant outstanding
Class of Warrant or Right [Line Items]
Warrants (in shares)	6,269,955
Class of warrant or right, exercise price of warrants or rights (in dollars per share) | $ / shares	$ 2.90
Honeywell Warrants | Investment Warrant outstanding
Class of Warrant or Right [Line Items]
Warrants (in shares)	10,631,633
Class of warrant or right, exercise price of warrants or rights (in dollars per share) | $ / shares	$ 1.89
Performance Warrant
Class of Warrant or Right [Line Items]
Warrants term (in years)	5 years
Class of warrant or right, exercise price of warrants or rights (in dollars per share) | $ / shares	$ 1.45
Proceeds from issuance of common stock and common stock warrants, net of issuance costs | $	$ 300,000
Additional performance warrants | $	$ 15,000
Number of trading days | tradingDay	15
Performance Warrant | UOP LLC | Related party
Class of Warrant or Right [Line Items]
Warrants term (in years)	5 years
Class of warrant or right, number of securities called by each warrant or right (in shares)	775,760
Exchange for pre-payment of equipment | $	$ 15,000

COMMON STOCK WARRANTS - Sched_2

COMMON STOCK WARRANTS - Schedule of Common Stock Warrant Activity (Details) - shares		6 Months Ended
	Oct. 08, 2021	Jun. 30, 2024	Jun. 30, 2023
Class of Warrant or Right [Roll Forward]
Warrants or rights at beginning of period (in shares)		29,151,075	11,473,727
Warrants issued (in shares)		0	0
Warrants exercised (in shares)		0	0
Warrants or rights at end of period (in shares)		29,151,075	11,473,727
Public Warrants
Class of Warrant or Right [Roll Forward]
Warrants or rights at beginning of period (in shares)		11,461,227	7,377,893
Warrants issued (in shares)		0	0
Warrants exercised (in shares)		0	0
Warrants or rights at end of period (in shares)		11,461,227	7,377,893
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
Private Warrants (excluding Earnout 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
SMUD Warrant outstanding
Class of Warrant or Right [Roll Forward]
Warrants or rights at beginning of period (in shares)		12,500	12,500
Warrants issued (in shares)		0	0
Warrants exercised (in shares)		0	0
Warrants or rights at end of period (in shares)		12,500	12,500
Investment Warrant outstanding
Class of Warrant or Right [Roll Forward]
Warrants or rights at beginning of period (in shares)		10,631,633
Warrants issued (in shares)		0
Warrants exercised (in shares)		0
Warrants or rights at end of period (in shares)		10,631,633
IP Warrant outstanding
Class of Warrant or Right [Roll Forward]
Warrants or rights at beginning of period (in shares)		6,269,955
Warrants issued (in shares)		0
Warrants exercised (in shares)		0
Warrants or rights at end of period (in shares)		6,269,955
Performance Warrants outstanding
Class of Warrant or Right [Roll Forward]
Warrants or rights at beginning of period (in shares)		775,760
Warrants issued (in shares)		0
Warrants exercised (in shares)		0
Warrants or rights at end of period (in shares)		775,760

STOCK-BASED COMPENSATION - Sche

STOCK-BASED COMPENSATION - Schedule of Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	$ 3,026	$ 2,725	$ 5,880	$ 4,784
Cost of revenue
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	415	0	1,339	0
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	908	1,130	1,309	2,123
Sales and marketing
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	163	165	258	315
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	$ 1,540	$ 1,430	$ 2,974	$ 2,346

STOCK-BASED COMPENSATION - Narr

STOCK-BASED COMPENSATION - Narrative (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Jan. 01, 2022	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of potential increase of shares authorized		5%		5%
Award vesting period				3 years
Unamortized stock-based compensation costs		$ 26,000		$ 26,000
Weighted average period of recognition for unamortized stock-based compensation costs				2 years 10 months 9 days
Total stock-based compensation		$ 3,026	$ 2,725	$ 5,880	$ 4,784
Tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights, percentage				25%
Tranche two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights, percentage				6.25%
2021 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Potential increase of shares authorized (in shares)		15,260,000		15,260,000
Increase in shares authorized for issuance (in shares)	8,700,000
Shares authorized for issuance (in shares)		26,310,000		26,310,000
Shares available for future grant (in shares)		5,376,809,000		5,376,809,000
Stock options | 2021 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period				4 years
Share expiration period				10 years
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum employee stock purchase amount				$ 25
ESPP purchase price of common stock, percent of fair market value				85%
Total stock-based compensation		$ 65	$ 90	$ 149	$ 149

STOCK-BASED COMPENSATION - Sc_2

STOCK-BASED COMPENSATION - Schedule of Share-based Payment Arrangement, Option and RSU Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Options Outstanding
Options outstanding at beginning of period (in shares)			2,598,382
Options granted (in shares)	0	0	0	0
Options released (in shares)			(48,867)
Options forfeited (in shares)			(10,972)
Options outstanding at end of period (in shares)	2,538,543		2,538,543		2,598,382
Options vested and exercisable (in shares)	1,936,099		1,936,099		1,775,256
Weighted average exercise price
Weighted average exercise price of options outstanding at beginning of period (in USD per share)			$ 1.33
Weighted average exercise price of options granted (in USD per share)			0
Weighted average exercise price of options released (in USD per share)			0.44
Weighted average exercise price of options forfeited (in USD per share)			0.54
Weighted average exercise price of options outstanding at end of period (in USD per share)	$ 1.35		1.35		$ 1.33
Weighted average exercise price of options vested and exercisable (in USD per share)	$ 1.17		$ 1.17		$ 1.10
Options, Additional Disclosures
Weighted average remaining contractual term of options outstanding			6 years 4 months 13 days		6 years 3 months
Weighted average remaining contractual term of options vested and exercisable			5 years 9 months 10 days		5 years 7 months 13 days
Aggregate intrinsic value of options outstanding	$ 807		$ 807		$ 1,422
Aggregate intrinsic value of options vested and exercisable	$ 756		$ 756		$ 1,198
RSUs
RSUs
Units outstanding at beginning of period (in shares)			13,162,368
Units granted (in shares)			11,851,132
Units released (in shares)			(2,579,523)
Units forfeited (in shares)			(2,661,399)
Units outstanding at end of period (in shares)	19,772,578		19,772,578		13,162,368
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)			$ 2.79
Weighted average grant date fair value per share of units granted (in USD per share)			0.94
Weighted average grant date fair value per share of units released (in USD per share)			2.09
Weighted average grant date fair value per share of units forfeited (in USD per share)			1.85
Weighted average grant date fair value per share of units outstanding at end of period (in USD per share)	$ 1.90		$ 1.90		$ 2.79

FAIR VALUE MEASUREMENTS - Sched

FAIR VALUE MEASUREMENTS - Schedule of Assets and Liabilities on Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Assets, Fair Value Disclosure [Abstract]
Short-Term Investments	$ 37,695	$ 87,899
Recurring
Assets, Fair Value Disclosure [Abstract]
Cash Equivalents and Restricted Cash	36,304	19,556
Short-Term Investments	37,695	87,899
Total Assets at Fair Value	73,999	107,455
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities measured at fair value	802	917
Recurring | Public common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Public common stock warrants	802	917
Recurring | Level 1
Assets, Fair Value Disclosure [Abstract]
Cash Equivalents and Restricted Cash	32,769	10,126
Short-Term Investments	21,132	54,681
Total Assets at Fair Value	53,901	64,807
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities measured at fair value	802	917
Recurring | Level 1 | Public common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Public common stock warrants	802	917
Recurring | Level 1 | Money market funds
Assets, Fair Value Disclosure [Abstract]
Cash Equivalents and Restricted Cash	10,200	10,126
Short-Term Investments	0	0
Total Assets at Fair Value	10,200	10,126
Recurring | Level 1 | U.S. Treasury securities
Assets, Fair Value Disclosure [Abstract]
Cash Equivalents and Restricted Cash	22,569	0
Short-Term Investments	21,132	54,681
Total Assets at Fair Value	43,701	54,681
Recurring | Level 2
Assets, Fair Value Disclosure [Abstract]
Cash Equivalents and Restricted Cash	3,535	9,430
Short-Term Investments	16,563	33,218
Total Assets at Fair Value	20,098	42,648
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities measured at fair value	0	0
Recurring | Level 2 | Public common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Public common stock warrants	0	0
Recurring | Level 2 | Certificate of deposit
Assets, Fair Value Disclosure [Abstract]
Cash Equivalents and Restricted Cash	77	77
Short-Term Investments	0	0
Total Assets at Fair Value	77	77
Recurring | Level 2 | U.S. agency securities
Assets, Fair Value Disclosure [Abstract]
Cash Equivalents and Restricted Cash		0
Short-Term Investments		12,447
Total Assets at Fair Value		12,447
Recurring | Level 2 | Commercial paper
Assets, Fair Value Disclosure [Abstract]
Cash Equivalents and Restricted Cash	3,458	9,353
Short-Term Investments	16,563	20,771
Total Assets at Fair Value	20,021	30,124
Recurring | Level 3
Liabilities, Fair Value Disclosure [Abstract]
Total liabilities measured at fair value	0	0
Recurring | Level 3 | Public common stock warrants
Liabilities, Fair Value Disclosure [Abstract]
Public common stock warrants	$ 0	$ 0

INCOME TAXES (Details)

INCOME TAXES (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Income Tax Disclosure [Abstract]
Income tax expense provision	$ 0	$ 0	$ 0	$ 0

GOVERNMENT GRANTS (Details)

GOVERNMENT GRANTS (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Government Assistance [Line Items]
Government Assistance, Current, Statement of Financial Position [Extensible Enumeration]	Prepaid expenses and other current assets		Prepaid expenses and other current assets
Production Tax Credits
Government Assistance [Line Items]
Government assistance amount	$ 54	$ 284	$ 54	$ 284
Current grants receivable	$ 1,100		$ 1,100		$ 800

REVENUE - Schedule of Revenue D

REVENUE - Schedule of Revenue Disaggregated by Source (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Disaggregation of Revenue [Line Items]
Revenue	$ 348	$ 2,827	$ 3,086	$ 3,199
Product revenue
Disaggregation of Revenue [Line Items]
Revenue	196	2,822	2,828	3,188
Service revenue
Disaggregation of Revenue [Line Items]
Revenue	61	5	78	11
Other revenue
Disaggregation of Revenue [Line Items]
Revenue	$ 91	$ 0	$ 180	$ 0

REVENUE - Schedule of Revenue C

REVENUE - Schedule of Revenue Contract Assets and Deferred Revenue (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Revenue from Contract with Customer [Abstract]
Contract assets	$ 126	$ 253
Deferred revenue	$ 20,089	$ 20,781

REVENUE - Narrative (Details)

REVENUE - Narrative (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2024	Dec. 31, 2023
Revenue from Contract with Customer [Abstract]
Contract assets increased	$ 127
Increase in deferred revenue	700
Advance payment	200
Revenue recognized	900
Deferred revenue, current	5,689	$ 2,546
Deferred revenue, non-current	$ 14,400

RELATED PARTY TRANSACTIONS (Det

RELATED PARTY TRANSACTIONS (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Related Party Transaction [Line Items]
Revenue	$ 348	$ 2,827	$ 3,086	$ 3,199
Deferred revenue, current	5,689		5,689		$ 2,546
Accounts receivable, net	981		981		1,990
Related party
Related Party Transaction [Line Items]
Revenue	6	1	530	2
Energy Warehouse Sales | Related party
Related Party Transaction [Line Items]
Revenue	6		500
Deferred revenue, current	27		27		1
Accounts receivable, net	87		87		29
Energy Storage Systems Sales | Related party
Related Party Transaction [Line Items]
Revenue		$ 1		$ 2
Honeywell ACS Ventures LLC | Related party
Related Party Transaction [Line Items]
Prepayment of equipment			14,400		600
Deferred revenue, non-current - related parties	$ 700		700		$ 700
Amortization			$ 27

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		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Numerator:
Net loss to common stockholders, basic	$ (21,940)	$ (22,929)	$ (40,250)	$ (44,830)
Net loss to common stockholders, diluted	$ (21,940)	$ (22,929)	$ (40,250)	$ (44,830)
Denominator:
Weighted-average shares outstanding – basic (in shares)	175,758,584	154,900,330	175,136,561	154,514,265
Weighted-average shares outstanding – diluted (in shares)	175,758,584	154,900,330	175,136,561	154,514,265
Net loss per share - basic (in USD per share)	$ (0.12)	$ (0.15)	$ (0.23)	$ (0.29)
Net loss per share - diluted (in USD per share)	$ (0.12)	$ (0.15)	$ (0.23)	$ (0.29)

NET LOSS PER SHARE - Schedule A

NET LOSS PER SHARE - Schedule Antidilutive Securities (Details) - shares	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of securities excluded (in shares)	51,462,196	26,662,110
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of securities excluded (in shares)	2,538,543	2,575,206
RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of securities excluded (in shares)	19,772,578	12,613,177
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of securities excluded (in shares)	29,151,075	11,473,727

SUBSEQUENT EVENTS (Details)

SUBSEQUENT EVENTS (Details)	Jul. 12, 2024 amendment $ / shares shares	Jul. 11, 2024 shares	Jun. 30, 2024 $ / shares shares	Dec. 31, 2023 $ / shares shares
Subsequent Event [Line Items]
Common stock, shares authorized (in shares) | shares			2,000,000,000	2,000,000,000
Common stock, par value (in USD per share) | $ / shares			$ 0.0001	$ 0.0001
Subsequent event
Subsequent Event [Line Items]
Number of possible amendments | amendment	6
Common stock, shares authorized (in shares) | shares	1,000,000,000	2,000,000,000
Common stock, par value (in USD per share) | $ / shares	$ 0.0001
Subsequent event | Reverse stock split one
Subsequent Event [Line Items]
Reverse stock split ratio, common stock	0.125000
Subsequent event | Reverse stock split two
Subsequent Event [Line Items]
Reverse stock split ratio, common stock	0.100000
Subsequent event | Reverse stock split three
Subsequent Event [Line Items]
Reverse stock split ratio, common stock	0.083000
Subsequent event | Reverse stock split four
Subsequent Event [Line Items]
Reverse stock split ratio, common stock	0.067000
Subsequent event | Reverse stock split five
Subsequent Event [Line Items]
Reverse stock split ratio, common stock	0.050000
Subsequent event | Reverse stock split six
Subsequent Event [Line Items]
Reverse stock split ratio, common stock	0.040000