🔋 Battery Runtime Calculator for Energy
Estimate usable runtime from battery capacity, reserve level, load and inverter losses.
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 = capacity × usable state-of-charge window × conversion efficiency ÷ average load
- Use nominal stored energy.
- Subtract the required reserve from starting charge.
- Apply conversion efficiency and divide by average load.
Worked example
Using these planning inputs:
- Battery capacity: 13.5 kWh
- Starting charge: 100 %
- Reserve charge: 20 %
- Average load: 800 W
- Inverter / system efficiency: 92 %
Estimated runtime: 12.42 h
Reality check: Changing load, inverter standby, temperature, ageing and maximum power can reduce actual runtime.
Method status and references
Energy-balance estimate. Use metered load and manufacturer limits for an operational decision; this calculation is a constant-load planning estimate.
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.