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Battery Life Calculator

How long a battery lasts from its capacity and the load current, with a usable-capacity allowance.

Enter values

Results update as you type.

Result

Runtime

11 h 20 min

Decimal hours
11.333
Days (continuous)
0.47
Usable capacity
1,700 mAh

About the Battery Life Calculator

How long a battery lasts from its capacity and the load current, with a usable-capacity allowance.

Also known as: battery runtime, how long will battery last, mah to hours, battery duration.

How to use this calculator

  1. Enter battery capacity, load current, usable capacity.
  2. The result updates instantly as you type — press Calculate (or Enter) at any time.
  3. Review the breakdown shown under the main result.
  4. Use Copy result or Share to save the answer or send a link with your inputs.

Formula

Runtime = capacity × usable fraction ÷ load current

Worked example

Using the values pre-filled in the calculator above:

  • Battery capacity = 2,000 mAh
  • Load current = 150 mA
  • Usable capacity = 85 %

the calculator returns:

  • Runtime: 11 h 20 min
  • Decimal hours: 11.333
  • Days (continuous): 0.47
  • Usable capacity: 1,700 mAh