Home Battery Backup Runtime Calculator

Estimate how long a battery could support an average essential load before reaching your chosen reserve. The calculation uses usable stored energy, average demand and reserve level; it does not assume that every appliance draws its nameplate power continuously.

WCL / INTERACTIVE MODEL

Usable battery capacity (kWh) Average backed-up load (kW) Reserve (%) Number of batteries

Why average load matters

A refrigerator, lights and internet may average far less power than central air conditioning, electric heat or an electric water heater. Peak-power capability is also separate from energy capacity. A battery can have enough kWh for several hours yet still be unable to start or run a high-power load if its inverter kW rating is too low, so check both energy and power limits.

Solar recharge is not included

This simple runtime estimate assumes no solar recharge during the outage. Actual solar-plus-storage systems can behave differently depending on weather, system design and backup controls.

Next step

Compare Home Battery vs Generator and review Solar Battery Cost.