Battery Runtime Calculator
Estimate constant-load runtime from nominal battery energy and an entered usable fraction.
Your result
EVERYDAYEnter your values and select calculate.
On this page How it works & practical examples
How to use the Battery Runtime Calculator
Use a usable percentage that accounts for discharge limits and power-conversion losses in your scenario. Watt-hours express energy, while watts express the load’s consumption rate.
The calculation
Worked example
12 V × 100 Ah gives 1,200 Wh nominal energy. Using 80% at a constant 100 W load gives 9.6 ideal hours.
Assumptions and limits
Nominal voltage and rated amp-hours do not capture every discharge condition. Temperature, battery aging, cutoff voltage and rate effects can change actual runtime. This is not a wiring or battery-safety specification.
Common questions
Can I enter a varying load?
Use a justified average for a rough estimate; the tool does not simulate a load profile.
Does 100% usable energy guarantee full rated capacity?
No. It is an ideal input assumption, not a measured property under every operating condition.