Battery life calculator

Run time = usable stored energy × delivery efficiency ÷ constant load power.

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Usable battery energy (Wh)

Load power (W)

More inputs and assumptions

Delivery efficiency (%)

Answer

…

Run time = usable stored energy × delivery efficiency ÷ constant load power.

More results

Precision and calculation record

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Rounding changes displayed numbers, not the calculation. Text, fractions, matrices and CSV schedules keep their own formatting. Automatic keeps up to 12 significant digits, with money shown to cents where applicable.

Step-by-step calculation

Inputs are substituted below. Each line evaluates the next operation; intermediate values are displayed to 12 significant digits while the calculation uses full precision.

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Formula and assumptions

Usable energy is your input, after any reserve. The model excludes standby draw, cold-weather loss, aging and changing loads; efficiency is an editable assumption.

Automatic precision shows numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.

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Updated 2026-09-26

Using Battery life calculator

Run time = usable stored energy × delivery efficiency ÷ constant load power.

Usable energy is your input, after any reserve. The model excludes standby draw, cold-weather loss, aging and changing loads; efficiency is an editable assumption.

Next: Electricity cost calculator

A worked example

With usable battery energy (wh) = 500, load power (w) = 100, delivery efficiency (%) = 90, the ideal run time (hours) is 4.5.

Next: Current calculator

Before you use the result

Usable energy is your input, after any reserve. The model excludes standby draw, cold-weather loss, aging and changing loads; efficiency is an editable assumption.

Example results for usable battery energy (wh)

These examples use Load power (W): 100; Delivery efficiency (%): 90. They are reference calculations, not recommended settings.

Usable battery energy (Wh)	Ideal run time (hours)
250	2.25
500	4.5
1000	9

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