Battery Life Calculator
Estimate how long a battery will last.
Result
How to use
- Enter your values in the fields above.
- Press Calculate to see your result instantly.
- Use the Share button to copy a link to your result.
About this calculator
This calculator estimates runtime as hours = capacity ÷ load — battery capacity in milliamp-hours (mAh) divided by the device's current draw in milliamps (mA), or watt-hours divided by power draw in watts for larger systems. It's a simplified model that assumes constant current and ignores the efficiency losses and voltage sag that real batteries show as they discharge.
Electronics hobbyists use it to size a battery for an Arduino or RC project before buying one, off-grid and solar system designers use the watt-hour version to match battery banks to expected loads, and it gives anyone a quick sanity check on a device's advertised battery life against its actual capacity and power draw.
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