Battery Life Calculator
Estimate runtime from a battery's capacity and a device's current draw.
Estimated runtime
8.5 h
8 h 30 min
Usage examples
Estimating how many phone charges a power bank gives
Use a power bank's capacity and a phone's average draw to estimate roughly how many charges it provides.
Predicting an IoT device's battery life
Enter a low-power sensor or IoT device's average current draw to estimate how often the battery needs replacing.
Estimating a drone or RC device's flight time
Use the battery capacity and average current draw to get a rough operating-time estimate.
Frequently asked questions
Can the actual runtime differ from this estimate?
Yes. This is a simple capacity-divided-by-current estimate adjusted by your efficiency figure. Real-world factors — battery chemistry, discharge rate, temperature, battery age — all affect actual runtime and can cause it to differ from this estimate.
Where does the 85% default efficiency come from?
There's no single correct number — real efficiency varies a lot by battery chemistry, discharge rate, and age. 85% is just a reasonable reference default; adjust it if you have a better figure for your specific battery or device.
Does switching between mAh/Ah or mA/A automatically convert the number?
Yes. Switching units converts the value to represent the same physical quantity rather than leaving the digits unchanged (e.g. 2000 mAh switched to Ah correctly shows 2 Ah).