Home Battery Backup for Power Outages: Sizing Guide (2026)
When the grid drops — a storm, a heat wave, or just an aging local line — a home battery keeps the fridge, lights and internet on. The usual mistake is sizing it by gut feel. Here is how to size it so it actually covers the days you need it.
1. List what you must keep running
Start with essentials, not the whole house. A fridge draws about 150W running with brief compressor surges. LED lights are 10-20W each. Router and internet sit around 10-15W. Add a well pump or sump pump if you have one, and medical devices first — those are non-negotiable.
2. Add up daily kWh
Multiply each load's watts by the hours it runs per day. A typical essential set — fridge 1.5kWh, lights 0.5kWh, internet 0.3kWh, phones and laptop 0.3kWh — totals about 2.6kWh/day. Add a 20% buffer and you are near 3kWh.
Example: essential-load day
- Fridge (150W × 10h effective): 1.5 kWh
- Lights (60W × 8h): 0.5 kWh
- Internet + phones (25W × 12h): 0.3 kWh
- Laptop (50W × 6h): 0.3 kWh
- Total + 20% buffer: ~3.1 kWh/day
3. Pick capacity and depth of discharge
LiFePO4 can safely use 90% of its rated capacity, versus 50% for lead-acid. For 3kWh needed daily, a 3.3kWh pack covers one day; for multi-day outages, double it. Our wall-mounted 5/10/15kWh units fit most homes without floor space drama.
4. Inverter and transfer
You need a pure sine wave inverter rated above the largest motor load's surge — a fridge or pump can pull 3-5x its running watts for a second at startup. An automatic transfer switch, or an all-in-one unit, switches over in under 20ms so the fridge doesn't reboot and spoil food.
5. Solar keeps it alive
For outages longer than a day or two, PV is what stops the battery from dying. A 1-2kW panel set recharges the pack during daylight and extends runtime for essentials almost indefinitely. Without solar, you are counting down a fixed reserve.
Building a home backup system?
Browse our wall-mounted and all-in-one LiFePO4 units — CE, UN38.3 certified, 6000-8000 cycle cells, with JK BMS and 5-year warranty.
Browse Products →Frequently asked
- How long will a 10kWh battery run my house in an outage? For essential loads (~2.6kWh/day) roughly 3 days; for whole-house use (~10kWh/day) about a day. LiFePO4 gives you 90% of that usable.
- Do I need solar to back up my home? Not for short outages. For anything longer than a day or two, panels are what keep the battery from flat-lining.
Published: October 2026. Figures are typical residential values; actual needs depend on your loads and climate.