Battery Life Calculator

Divide capacity by current draw, both in the same milli unit, then multiply by an efficiency factor. Hours = (mAh / mA) x (efficiency / 100).

Rated capacity assumes an ideal slow discharge. Voltage regulators, heat and faster discharge mean you rarely get the full rating, so an 85% factor gives a more honest estimate.

Use the average current over the use you care about. A device that idles and bursts will last longer than its peak draw suggests, so average across a realistic cycle.

For a runtime estimate in hours, capacity in mAh and draw in mA already share the same voltage assumption, so the volts cancel out. Use watt-hours only when comparing across voltages.

A device drawing no current would run forever, which is not a meaningful estimate, so a current draw greater than zero is required.