🔋 Battery Runtime Calculator for Solar & Energy
Estimate backup runtime for a constant load.
This free tool helps you turn project measurements into a practical planning estimate. Enter values in Vaelden’s interactive calculator, review the result, and confirm important assumptions against supplier data, measurements, codes or qualified advice before committing materials or money.
Open the Battery Runtime calculator →
How to calculate battery runtime
Method: Runtime = nominal capacity × usable fraction × conversion efficiency ÷ average load
- Use the battery’s usable energy limit, not only its nameplate capacity.
- Total the average critical load that will actually remain connected.
- Check the result against inverter continuous and surge limits.
Worked example
Using these planning inputs:
- Battery capacity: 13.5 kWh
- Usable capacity: 90 %
- Average load: 0.8 kW
- Conversion efficiency: 90 %
Estimated runtime: 13.7 h
Reality check: Heating, motors, pumps, refrigeration cycles, temperature and battery ageing can shorten real runtime.
Method status and references
Energy-balance estimate. Nameplate energy and delivered power are different constraints. Confirm both against the battery and inverter data sheets.
Before you calculate
Use consistent units and the best measured inputs available. Real materials, equipment, site conditions and tolerances can change the result. Vaelden shows planning estimates; regulated, structural, electrical, plumbing, pressure and other safety-critical work still requires appropriate local compliance and professional advice.