How to size a home battery: a 5-minute method
Daily consumption, backup hours and peak load — three numbers that decide how many kWh and kW you really need.
By Xinya Power editorial team
Over-sizing a home battery wastes money; under-sizing leaves you in the dark at 9 pm. Three numbers are enough for a first estimate.
1. Evening and night consumption
Look at the bill or smart-meter data and estimate how many kWh you use after the sun goes down. For many homes that is 40–60% of daily consumption.
2. Backup hours
How long must essential loads — lights, fridge, router, a pump — run during an outage? Multiply their power by the hours. This is often smaller than people expect.
3. Peak load
The largest power drawn at once (kW) decides the inverter, not the battery. An air-conditioner starting while the kettle boils can briefly exceed 4 kW.
Put it together
Usable capacity ≈ max(evening use, backup energy) ÷ 0.9. A household using 8 kWh in the evening needs roughly 9–10 kWh usable — two 5.12 kWh stackable modules, or one 10.24 kWh unit. Because the modules stack, you can start with one and add another when you buy an EV.
Try the configurator on our home page, then ask our engineers to confirm the inverter and cabling.
