Battery Life Calculator
Estimate how long a battery will power your device. Enter capacity and current draw, and get runtime in hours, days of use, and the capacity needed for a target runtime.
Use 1 for lithium batteries; 1.1 to 1.3 for lead-acid.
Lead-acid: about 50%. Lithium: 80 to 100%.
Capacity needed to reach this runtime.
Estimated runtime
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Enter capacity and current draw.
Days of use
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mAh needed for target runtime
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Note: this is an estimate. Real runtime varies with temperature, battery age, discharge efficiency and how steady the current draw is.
How to use
- Enter the battery capacity in milliamp-hours (mAh) from its label.
- Enter how much current your device draws in milliamps (mA).
- Adjust the Peukert exponent and usable-capacity percentage for your battery type.
- Read the estimated runtime, days of use at your daily hours, and the mAh needed for any target runtime.
How the math works
Runtime in hours = usable capacity (Ah) divided by current draw (A), adjusted with the Peukert exponent for heavy loads: time = C / I^n. Days of use = runtime hours / hours used per day. Reversing the formula gives the capacity needed for a target runtime.