Summary of Significant Accounting Policies - Narrative (Details)	12 Months Ended
	Dec. 31, 2024 USD ($) platform	Dec. 31, 2023 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of primary battery platforms | platform	1
Restricted cash and cash equivalents included in other assets	$ 1,300,000	$ 56,000.0
Impairment losses	0	0
Warranty liability	0	0
Revenue	$ 24,167,000	$ 9,053,000
Stock options | Equity Incentive Plans
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Award vesting period (in years)	4 years
Three customers | Accounts receivable | Customer concentration risk
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Concentration risk percentage		80.00%
Customer one | Revenue benchmark | Customer concentration risk
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	$ 5,400,000	$ 3,300,000
Customer two | Revenue benchmark | Customer concentration risk
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	$ 2,800,000	1,500,000
Customer two | Accounts receivable | Customer concentration risk
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Concentration risk percentage	50.00%
Customer three | Revenue benchmark | Customer concentration risk
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	$ 2,800,000	1,100,000
Money market funds | Level 1
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash equivalents	$ 23,500,000	$ 36,700,000