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Battery runtime.

Estimate how long a battery will power a constant load.

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01 / QUESTION

An ideal 12 V, 10 Ah battery stores approximately:

Nominal energy = 12 V × 10 Ah = 120 Wh before losses.

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How the calculation works

Hours ≈ (Ah × V × usable fraction × efficiency) ÷ load power (W).

KEY FORMULAHours ≈ (Ah × V × usable fraction × efficiency) ÷ load power (W).
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Worked example

A 12 V, 100 Ah battery at 80% usable capacity and 90% efficiency with a 120 W load lasts about 7.2 hours.

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Before you rely on this result

Real capacity depends on chemistry, temperature and discharge rate. This is only an estimate.

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Informational tool. It does not replace testing, measurement or professional advice when needed.

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Frequently asked questions

Why is efficiency included?+

Inverters and converters lose some of the available energy.

Can I use it for solar batteries?+

Only as a first estimate. Full solar design requires load profiles and protection analysis.