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Battery life calculator
How many hours a battery lasts for a given load, with a safety margin.
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- Works on any device
About Battery life calculator
Estimate how many hours a battery will run a device. The basic formula is capacity in mAh divided by the load current in mA. Real batteries rarely deliver their full rating, so a safety margin is applied. It helps size packs for sensors, Arduino projects, and power banks.
How to use Battery life calculator
- Enter the battery capacity.
- Enter the load current or power and a safety margin.
- Read how many hours the battery should last.
Why use this tool?
- Private: everything happens in your browser. Nothing you enter is uploaded.
- Free, with no sign-up, no watermark and no limit on how often you use it.
- Works on phones, tablets and computers: Android, iPhone, Windows, Mac and Linux. Nothing to install.
- Free to embed on your own website, with a ready-made code to copy.
- Available in 10 languages.
Also known as
Frequently asked questions
How do I convert mAh to hours of runtime?
Divide the battery capacity in mAh by the device current in mA. A 2000 mAh battery powering a 100 mA load lasts about 20 hours before margin.
Why add a safety margin?
Real batteries rarely deliver their full rating. Age, temperature and discharge rate reduce usable capacity, so a margin gives a more realistic runtime.
Can I use the full battery capacity?
Often not. Many batteries should not be drained fully, for example lead acid and lithium cells. The margin lets you leave some capacity unused.
Is Battery life calculator free?
Yes. Battery life calculator on Toolipedia is free to use, with no sign-up and no watermark.
Is it safe to use?
Yes. Everything is worked out in your browser, and nothing you enter is sent to our server.
Does it work on my phone?
Yes. It works in any modern browser on Android and iPhone, as well as on tablets and computers. There's nothing to install.
Do I need an account?
No. Just open the page and use the tool. There's no sign-up and no email needed.
Can I put Battery life calculator on my own website?
Yes. Use the Embed on your site button under the tool to copy a short piece of code and paste it into your page. It is free, needs no account, and the tool keeps working inside your page.