Electrical

Battery Runtime Calculator

Estimate battery runtime or required amp-hour capacity for a constant load. Compare SI/US results and review the method, assumptions and related references below.

Change any input to update the calculation. Unit changes preserve the physical quantity.

CALCULATION SETUP

Inputs

Preset

Nominal battery voltage

Nominal battery capacity

Load entry

Useful load power

Need an input value?

Single & Three-Phase Power Reference ↗AC load real power only; battery supply voltage/capacity remain your inputs.

Usable depth of discharge

Reserve of usable energy

Conversion efficiency

Calculated locally in your browser. No sign-up or input upload.

YOUR CALCULATION

Results

Estimated runtime

3.888 h233.28 min

Required / entered capacity

100 Ah

Nominal stored energy

1.2 kWh

Useful load energy

0.7776 kWh

Useful load power

200 W

Battery-side power

222.2222 W

Calculation breakdown

Result interpretation: Estimate battery runtime or required amp-hour capacity for a constant load

Assumptions & checks

Nominal-energy estimate; discharge curves, Peukert effect, aging, temperature, voltage sag and startup surges excluded. Verify manufacturer discharge data.

Formula

Estimate battery runtime or required amp-hour capacity for a constant load

Useful energy=V·Ah·3600·DoD·(1−reserve)·η; runtime seconds=useful joules/load watts. Reverse Ah=runtime·load/(3600·V·usable fraction). Worked example: 12 V × 100 Ah, 80% usable, 10% reserve and 90% efficiency provides 777.6 Wh to a 200 W load: 3.888 h.

Worked example

Using the default values shown in the calculator, the same formula gives the following result. This is a quick sanity check for the calculation, not a design recommendation.

Inputs

Nominal battery voltage: 12 V
Nominal battery capacity: 100 Ah
Load entry: Useful load power
Useful load power: 200 W
Usable depth of discharge: 80 %
Reserve of usable energy: 10 %
Conversion efficiency: 90 %

Result

Estimated runtime: 3.888 h
Required / entered capacity: 100 Ah
Nominal stored energy: 1.2 kWh
Useful load energy: 0.7776 kWh
Useful load power: 200 W
Battery-side power: 222.2222 W

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Technical references for this calculation

Reference lookupSingle & Three-Phase Power Reference Reference lookupWire Resistance Chart

Frequently asked questions

What does this result tell me?

Nominal-energy estimate; discharge curves, Peukert effect, aging, temperature, voltage sag and startup surges excluded. Verify manufacturer discharge data.

How can I check the calculation?

Worked example: 12 V × 100 Ah, 80% usable, 10% reserve and 90% efficiency provides 777.6 Wh to a 200 W load: 3.888 h. Review each stated input and unit; use project-specific values rather than treating the editable example as a requirement.

Reference data & method sources

NIST SI conversion factors
SI/US dimensional conversions. Geometry and energy balances are stated explicitly, not attributed to a design standard.