How Long Will a 300Ah Battery Last?

Answer
29.2 h at 100 W (LiFePO4)

A 12 V 300 Ah battery stores 3,600 Wh. Using 90% of a LiFePO4 battery through a 90% efficient inverter leaves 2,916 Wh, enough for 29.2 hours at 100 W. Lead-acid gives about half that because only 50% should be used.

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How we calculated this

    For estimating and educational purposes only. Results are approximate and are not a substitute for a licensed professional, the manufacturer's instructions or your local code. Disclaimer

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    Runtime by load (12 V, through a 90% inverter)

    LoadLiFePO4 (90% usable)Lead-acid (50% usable)
    25 W116.6 h64.8 h
    50 W58.3 h32.4 h
    100 W29.2 h16.2 h
    200 W14.6 h8.1 h
    300 W9.7 h5.4 h
    500 W5.8 h3.2 h
    1000 W2.9 h1.6 h

    Lead-acid runtimes at high loads are optimistic because of the Peukert effect.

    Frequently asked questions

    Can a 300Ah battery run a refrigerator?

    A 12 V fridge averaging 50 W would run about 65 hours on lithium (no inverter needed for a 12 V fridge).

    How many watt-hours is 300Ah?

    3,600 Wh at 12 V, or 3,840 Wh for a 12.8 V LiFePO4 battery.

    Open the full calculator: Battery Runtime Calculator →