Home Battery Runtime Estimator

The energy your loads use in a day is the running watts of each load, times its quantity, times the hours a day it runs, added up and divided by 1,000 to give kilowatt-hours. The average load is that energy spread over 24 hours.

The energy available is the number of units times the energy per unit, less the reserve you keep and any derate you enter. The runtime is the energy available divided by the average load, and the units for your target are the target hours times the average load, divided by what one unit gives after the reserve and the derate, rounded up.

Two checks follow. The running load, everything on at once, must fit within the continuous output of the units entered, and the starting peak, where the largest motor starts while everything else runs, must fit within their peak output.

A worked example from our own generator FAQ: a single home battery typically stores 10 to 15 kilowatt-hours, which runs a modest 5 kilowatt load for about two to three hours. With no reserve, the estimator gives 2 hours for 10 kWh and 3 hours for 15 kWh at a steady 5 kW.

Typical figures: the site's generator sizing guide and general practice; the nameplate or spec sheet governs. The battery's figures are the ones you enter from its datasheet. A licensed electrician's load assessment on site decides the size of a battery system.