REFERENCE // TOOL
Battery Runtime
Usable energy in a battery and how long it lasts under a given load.
Work out the usable energy in a battery and how long it lasts under load. The usable share depends on the chemistry.
Runtime
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Rated capacity
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Usable (after DoD + losses)
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Formula
runtime = (rated Wh × depth-of-discharge × efficiency) ÷ load watts. Use rated amp-hours, not a battery's cold-cranking-amp rating. Use ~100% efficiency for a DC load straight off the battery, ~85% through an inverter. Motors need about 3× their running watts to start — that sizes the inverter, not the runtime.
Source: When the Power Goes Out (OSU Extension EM 8734) · RELiON & Anern depth-of-discharge figures (2025).