Why inverter capacity and battery capacity are different

An inverter converts DC battery power to AC for loads. Its kW rating limits the power it can deliver at once. Battery capacity in kWh limits the energy available over time. Neither number replaces the other.

Use a two-part check

First estimate simultaneous essential load and starting surge. That tests inverter power. Then multiply the load by required hours and adjust for usable battery capacity and efficiency. That tests battery energy. Use the load calculator before the battery calculator.

A backup design also needs protections, wiring, charging capability and manufacturer compatibility. For long or frequent outages, use the battery versus generator comparison as a cash-cost screen, not a substitute for design.