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.
How to use Battery Life Calculator
- Enter the battery capacity in mAh.
- Enter the average current the device draws in mA.
- Read the estimated runtime in hours or days.
- Apply a safety margin for real-world losses.
Frequently asked questions
How does the calculator estimate battery runtime?
It divides the battery capacity in mAh by the device current draw in mA to get the number of hours before the battery is flat.
Why is the real runtime often shorter than the estimate?
Batteries rarely deliver their full rated capacity under load, so the tool gives an ideal figure that you should derate for temperature, age and cutoff voltage.
Can it show days as well as hours?
Yes, for low-current devices it converts the hours figure into days so long-running gadgets are easier to read.
What is 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.
Is Battery Life Calculator free to use?
Yes. Battery Life Calculator is completely free, with no sign-up and no usage limits.
Does Battery Life Calculator work in a web browser?
Yes. Battery Life Calculator runs in any modern web browser. There is nothing to download or install.
Is my data private with Battery Life Calculator?
Yes. Battery Life Calculator runs entirely on your device in your browser, so nothing you enter is uploaded to a server.
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