Battery Life Calculator

Wondering how long a battery will power your project or gadget? This calculator estimates the runtime from two numbers: the battery capacity in milliamp hours and the average current your device draws in milliamps. Divide capacity by current draw and you get the ideal runtime in hours, but real batteries never deliver their full rating, so the tool also applies a realistic efficiency factor to give a practical estimate. It converts the result into hours, and days where useful, so you can plan how often you will need to recharge or swap cells. This is handy for sizing a battery for a microcontroller build, an LED strip, a portable speaker or a sensor node. Enter your capacity, your load, and an efficiency you trust, then read both the theoretical and realistic runtime instantly. Everything runs locally in your browser.