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Battery runtime, load by load.
Estimate how long a steady AC load can run after the battery reserve and inverter losses you choose are accounted for.
Inputs
Runtime estimate
Formula and caveats
Runtime = battery kWh × usable percentage × inverter efficiency × 1,000 ÷ load watts. This assumes the load is steady and that the battery can deliver its rated capacity at that discharge rate.
Real runtime can be shorter because of temperature, battery age, power-management cutoffs, conversion losses outside the inverter and startup surges. For a critical backup system, use the manufacturer's usable-energy figure and an electrician's load calculation.