battery tool
Battery Runtime Calculator
Estimate usable battery runtime from capacity, load, and efficiency.
Runtime = usable battery Wh ÷ connected load. DoD and inverter efficiency are explicit estimates, not guarantees of real-world performance.
Estimated battery runtime
17.3 hours
Usable energy: 8640 Wh.
Battery runtime guide
Estimate runtime from usable battery energy
This calculator estimates how long a connected load may run from a battery after accounting for voltage, depth of discharge, and inverter efficiency. It is a planning estimate, not a guaranteed runtime.
How the calculation works
Amp-hours describe charge capacity, while watt-hours describe energy. The calculator first estimates usable energy, then divides by the connected load.
usable Wh = Ah × V × DoD × inverter efficiency
runtime = usable Wh ÷ load W
Worked examples
Small load: 100 Ah × 12 V × 80% DoD × 90% efficiency = 864 usable Wh. At 100 W, the estimate is 8.64 hours.
Larger load: 100 Ah × 12 V × 80% DoD × 90% efficiency = 864 usable Wh. At 500 W, the estimate is about 1.73 hours.
Practical considerations
Battery chemistry, age, temperature, discharge rate, inverter efficiency, wiring, battery-management limits, and manufacturer recommendations can all change actual runtime. Keep the assumptions visible and use equipment documentation when available.
Frequently asked questions
What does battery runtime depend on?
The estimate depends on battery amp-hours, voltage, depth of discharge, inverter efficiency, and connected load in watts.
Why is usable capacity less than the battery label?
The calculation reduces nominal stored energy by the selected depth of discharge and inverter efficiency assumptions.
Why can real runtime be different?
Chemistry, age, temperature, discharge rate, inverter behavior, wiring losses, and manufacturer limits can change real performance.
Does a higher voltage always mean longer runtime?
Voltage changes the watt-hours represented by a given Ah rating. Runtime also depends on the connected load and the usable fraction of the battery.
Important assumptions
This is a planning estimate, not a guarantee of performance. Real equipment varies with temperature, age, power quality, duty cycle, wiring, and manufacturer specifications.