Battery Lifetime Calculator
Enter the known values and run the calculation.
Enter the battery capacity in amp-hours, then enter the expected current draw and choose whether that current is in amps or milliamps.
Run the calculation to get the estimated operating time in hours. Use that result as a planning number, not as a guaranteed discharge duration.
Overview
Estimate expected run time from capacity and current draw for practical power budgeting.
Use this tool to estimate how long a battery can support a stated load current before it reaches the end of its nominal usable capacity.
Use it for quick power budgeting, portable-device planning, and bench estimates before you do a chemistry-specific runtime analysis.
The math and how it's used
Capacity is treated in amp-hours and current is normalized to amps before the division.
This is a first-pass runtime estimate. Real cells shift with discharge rate, cutoff voltage, chemistry, and temperature.
In practice, this is the back-of-the-envelope runtime number you reach for when a portable setup, backup rail, or battery-powered fixture needs a quick sanity check.
It assumes average current draw and usable rated capacity. Pulse loads, cold temperature, aging, cutoff-voltage limits, and converter losses can all move the real runtime by a noticeable amount.
What to watch
This relationship assumes the rated capacity is fully usable at the stated load. Real batteries lose effective capacity when discharge rate, age, temperature, or cutoff voltage changes.
If runtime margin matters, compare the result against the actual discharge curve for the battery chemistry and the duty cycle of the load.