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DIY Cost Tools

DIY Cost Tools

Battery Runtime Calculator

Estimate usable battery energy and runtime from nominal voltage, amp-hours, allowed depth of discharge, efficiency, and load.

Use the units shown beside each field. Decimal and scientific notation are accepted for non-integer fields; blanks, commas, fractions and non-finite entries are rejected.

Nominal battery energy1280 Wh
Estimated usable energy921.6 Wh
Estimated runtime3 h 4 min 19.2 sec
Estimated runtime3.072 hours

The displayed results apply to the default example. Enable JavaScript to calculate other inputs.

How to use this calculator

  1. Replace the example values with measurements or ratings for the exact vehicle, circuit, component or system.
  2. Keep every value in the labeled unit and use manufacturer data where available.
  3. Select Calculate, then review the result together with the limitations and safety notes.

Formula and method

Nominal Wh = volts × amp-hours. Usable Wh = nominal × usable-depth rate × efficiency. Runtime = usable Wh ÷ average watts.

Calculations run in your browser. Results are hidden whenever an input changes or validation fails, preventing an older result from being mistaken for a new calculation.

Worked example

Battery voltage = 12.8 V; Battery capacity = 100 Ah; Usable depth of discharge = 80 %; System efficiency = 90 %; Average load = 300 W. The calculator returns Nominal battery energy = 1280 Wh; Estimated usable energy = 921.6 Wh; Estimated runtime = 3 h 4 min 19.2 sec; Estimated runtime = 3.072 hours.

The worked example uses the same defaults shown in the interface, allowing the formula and displayed result to be checked together.

Limitations and safety

Battery voltage, temperature, age, discharge rate, chemistry, inverter cutoff and load variation affect real capacity. Follow battery and equipment specifications.

This is an educational planning model. Confirm ratings, tolerances, code requirements and safe procedures with manufacturers and qualified professionals before purchasing, modifying, wiring or operating equipment.

Frequently asked questions

Why is runtime lower than volts times amp-hours divided by watts?

The model reserves part of the battery and applies efficiency losses before dividing usable energy by the load.

Why does the calculator reject my entry?

Each field shows its supported range. Whole-number fields reject decimals, and all fields reject blanks, words, comma-formatted numbers, fractions and non-finite values.

How should I use the displayed precision?

Keep extra digits while checking the calculation, then round to the precision supported by the measurements, component tolerances and published ratings.

Review notes and reference

Reviewed October 4, 2026. The formula and default example were checked together. The script was tested for defaults, input boundaries, invalid formats, condition-specific errors and recovery after an error. Reference: OSHA electrical safe-work requirements. Explanations and examples are original.

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