Battery Life Calculator
Estimate how long a battery will last by dividing its capacity in milliamp-hours by the average current draw of the device in milliamps.
- Realistic estimate (×0.75)
- 6.00 hours
Formula: Life = Capacity (mAh) / Current (mA)
About Battery Life Calculator
Battery Life Calculator is a free online calculator that gives you an instant, accurate result as you type. Estimate how long a battery will last by dividing its capacity in milliamp-hours by the average current draw of the device in milliamps.
The calculation uses the standard formula Life = Capacity (mAh) / Current (mA) and updates live with every change to the inputs. Everything runs client-side in your browser — fast, private, and free to use as often as you like.
Real-world battery life is usually 70-80% of the theoretical value because capacity drops with high discharge rates, cold temperatures and age.
Frequently Asked Questions
Is Battery Life Calculator free to use?
Yes. Battery Life Calculator is completely free, with no sign-up, no downloads, and no usage limits. You can use it as many times as you like on any device with a web browser.
How accurate is this calculator?
The calculator applies the standard formula (Life = Capacity (mAh) / Current (mA)) with full floating-point precision and rounds only the displayed result. For most practical purposes the results are exact.
Why does my device die sooner than calculated?
Rated capacity assumes a slow, steady discharge at room temperature. High peak currents, cold weather and battery aging all reduce usable capacity.
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