Battery life calculator
Useful for sensors, electronics projects and portable devices. Enter the capacity and the average current.
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Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter battery capacity, average device current and usable capacity.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Runtime (h) = capacity (mAh) × usable % ÷ 100 ÷ current (mA).
Example
Inputs: Battery capacity = 2,000 mAh, Average device current = 100 mA, Usable capacity = 100 %. Result: Runtime: 20 h; In days: 0.833 days; Hours:minutes: 20:00.
Limits and caveats
- Real capacity falls with high current, cold and ageing; use 70 to 80% for a realistic estimate.
- If the device sleeps and wakes, enter the average current, not the peak.
Questions about this tool
How long does a 2000 mAh battery last at 100 mA?
20 hours in theory. With 80% usable capacity it is about 16 hours.
How do I find the average current of a sleeping device?
Multiply each current by its share of time and add them. For example 20 mA for 1% of the time and 0.01 mA otherwise gives about 0.21 mA.
Does it work for Ah batteries?
Yes, multiply Ah by 1000 to get mAh, or use the inverter battery calculator for loads in watts.