Battery Runtime Calculator
Estimate battery runtime from voltage, amp-hour capacity, load power, and a usable-energy efficiency factor.
Your result
Review your calculated values below.
Ready when you are.
Choose Calculate to see your result.
How to use this calculator
- Enter your values in the labeled fields, keeping the displayed units.
- Choose Calculate or press Enter in a single-line field.
- Review the result and the assumptions below before using it.
Formula and method
Usable Wh = voltage × amp-hours × usable factor / 100. Runtime hours = usable Wh / load watts.
Worked example
A 12 V, 10 Ah battery with an 80% usable factor supplies a 24 W load for about four hours.
What the result assumes
Combine discharge limits and conversion losses in the usable factor. Temperature, aging, load variation, and discharge-rate effects can reduce runtime.
Common question
Can I enter a capacity given in mAh?
Divide milliamp-hours by 1,000 first. For example, 5,000 mAh equals 5 Ah at the stated battery voltage.