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Battery Life Calculator

Enter the battery capacity, the load and a depth of discharge limit to get the runtime and a discharge curve.

Battery life calculator

Runtime: —
Usable capacity: —
Load current: —
Energy delivered: —
—
Runtime is the usable amp hours divided by the load current, using the depth of discharge limit you set.

How to use the Battery Life Calculator

  1. Enter the battery capacity in amp hours and the system voltage.
  2. Choose whether the load is given in amps or watts, then type the load.
  3. Set the depth of discharge limit and read the runtime and discharge curve.

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Frequently Asked Questions

Common questions about the free online battery life calculator.

Divide the usable amp hours by the load current in amps. A 100 amp hour battery at 80 percent depth of discharge gives 80 usable amp hours.
Runtime in hours equals the capacity in amp hours times the depth of discharge, divided by the load current in amps.
Divide the load in watts by the system voltage to get amps, then apply the same runtime formula with that current.
It is the share of the battery capacity you are willing to use. Lead acid batteries are usually limited to 50 percent, lithium to about 80 or 90.
Real runtime is lower because of the Peukert effect, temperature, inverter losses and battery ageing, so treat the result as a best case.
Yes. A battery rated at the 20 hour rate delivers less total energy when discharged quickly, which is why the discharge curve falls away.
Multiply the amp hours by the system voltage. A 100 amp hour battery at 12 volts stores about 1200 watt hours of energy.
No. Deep discharging shortens battery life, so leave a margin and recharge soon after the battery reaches the limit you set.
No. The runtime is calculated in your browser, so the capacity and load figures you enter stay on your own device.
Yes. It is completely free, needs no account, and you can compare as many batteries and loads as you wish.

Last updated: October 10, 2026