Calculate battery run time in hours from capacity in Ah, mAh or Wh and the load in watts or amps, or find the amp-hour capacity a load needs.
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Battery Run Time Formula
The following ideal equation estimates battery run time at constant nominal voltage and load power, with usable capacity and delivery efficiency both set to 100%. The calculator also supports editable loss assumptions.
- Where T is the time in hours
- Where C is the capacity (Ah)
- V is voltage (volts)
- LP is the load power (watts)
Multiply capacity in amp-hours by nominal volts to obtain watt-hours, apply the usable fraction and delivery efficiency, then divide by load watts. When entering measured battery-side current, runtime is usable amp-hours divided by battery amps; do not apply conversion efficiency again.
Battery Run Time Definition
A battery run time is the total time in hours that a battery can sustain a certain power output.
Battery Run Time Example
The following is an example of how to calculate a total battery run time.
- First, determine the battery capacity. This is the rated charge capacity of the battery in amp-hours. For this example, we will say that value is 100 Ah.
- Next, determine the power output. This power output is also known as the usage rate and is measured in watts. We will say 50 watts for this problem.
- Finally, assume a nominal battery voltage of 10 V. With 100% usable capacity and 100% delivery efficiency, 10 * 100 / 50 = 20 hours. Using the calculator’s editable 80% usable-capacity and 90% efficiency assumptions gives 14.4 hours.
FAQ
Battery run time is the total amount of time a battery can sustain a certain power output. This run time will depend on several factors including discharge %, battery size, type of battery, and many more.
