For the three months ended June 30, 2023 and 2022, cost of revenue was $1,693,318 and $423,672, respectively, representing an increase of $1,269,646 or 300%. The increase corresponds to the increase in our revenue during the period, and consisted primarily of $1,076,003 of costs incurred to procure customized finished goods and component materials for a new product line, an increase of $116,533 in depreciation expense due to revenue generating equipment placed in service, and increased labor costs of $54,609. The gross margin percentage was 37% and 28% for the three months ended June 30, 2023 and 2022, respectively.
For the six months ended June 30, 2023 and 2022, cost of revenue was $2,809,732 and $546,590, respectively, representing an increase of $2,263,142 or 414%. The increase corresponds to the increase in our revenue during the period, and consisted primarily of $1,984,380 of costs incurred to procure customized finished goods and component materials for a new product line, an increase of $148,411 in depreciation expense due to revenue generating equipment placed in service, and increased labor costs of $99,127. The gross margin percentage was 37% and 31% for the six months ended June 30, 2023 and 2022, respectively.
Research and Development
Research and development (“R&D”) includes expenses incurred in connection with the R&D of our CFV thermal management solution, high-areal-capacity battery electrodes, 3D engineering for a rechargeable battery and non-cash stock-based compensation expenses. Research and development expenses are charged to operations as incurred.
For the three months ended June 30, 2023 and 2022, R&D expenses were $1,408,079 and $999,484, respectively, representing an increase of $408,595 or 41%. The increase during 2023 was comprised primarily of $518,908 related to planned increases in headcount in order to build future capacity, partially offset by a reduction in R&D costs of $158,500 related to a decline in outsourced R&D costs.
For the six months ended June 30, 2023 and 2022, R&D expenses were $2,796,294 and $1,720,831, respectively, representing an increase of $1,075,463 or 62%. The increase during 2023 was comprised primarily of $1,079,372 related to planned increases in headcount in order to build future capacity, rent expense of $30,782 for a new facility for R&D initiatives designed to build future revenue growth, partially offset by a reduction in R&D costs related to a decline in outsourced R&D costs.
We expect that our R&D expenses will increase as we expand our future operations.
Selling, General and Administrative
Selling, general and administrative expenses consisted primarily of cash and stock-based compensation, payroll taxes and other benefits, consulting fees, registration fees, office expenses, rent expense, directors and officers insurance, travel and entertainment, marketing and advertising, and filing fees.
For the three months ended June 30, 2023 and 2022, selling, general and administrative expenses were $5,591,516 and $4,326,162, respectively, representing an increase of $1,265,354, or 29%. The increase is primarily due to increases in labor costs of $442,414, depreciation expense of $400,842 due to the completion of automation equipment and enhancements to the facility, consulting fees of $251,626, travel costs of $180,699 for conferences and customer visits to build future revenue growth, costs related to the acquisition of vibration technology of $125,000, partially offset by a decrease in marketing and advertising expenses of $184,501, and a decrease of $106,475 in stock-based compensation.
For the six months ended June 30, 2023 and 2022, selling, general and administrative expenses were $11,107,407 and $7,861,085, respectively, representing an increase of $3,246,322, or 41%. The increase is primarily due to increases in labor costs of $1,449,895, depreciation expense of $599,817 due to the completion of automation equipment and enhancements to the facility, consulting fees of $462,391, marketing and advertising expenses of $342,906, $316,817 related to travel and conferences to build future revenue growth, costs related to the acquisition of vibration technology of $250,000, partially offset by a decrease of $437,294 in stock-based compensation.
Other Income (Expense)
For the three months ended June 30, 2023 and 2022, other expense, net was $337,585 and $92,913, respectively, representing an increase of $244,672, or 263%. The change is primarily attributable to an additional $154,736 for interest recorded in connection with the Prepaid Advance, an additional $111,335 for amortization of debt discount in connection with the Prepaid Advance, partially offset by a $21,399 change in the fair value of accrued issuable equity.