Home Battery Buying Guide: kWh, Chemistry, and Backup
For essentials backup, fridge, lights, internet, most homes need about 10–20 kWh. For whole-home backup with HVAC, plan on 20–40+ kWh, usually two or more batteries. Size it from the loads you want to run and how long an outage you want to cover.
How many kWh do you need?
Start from your loads, not the product. Essentials, refrigerator, lights, phones, internet, a few outlets, draw roughly 5–10 kWh per day. Add central air, electric heat, or a well pump and daily use jumps to 20–40+ kWh. Backup runtime is simply usable capacity divided by your load in kilowatts.
Whole-home vs essentials backup
Whole-home backup powers everything through the main panel and needs the most capacity. Essentials (critical-loads) backup wires a chosen subset, fridge, lights, outlets, internet, to a small subpanel, so the same battery lasts far longer. Most single-battery installs are essentials setups; whole-home backup usually means two or three batteries.
Battery chemistry: LFP vs NMC
Most 2026 home batteries use lithium iron phosphate (LiFePO4, or LFP). LFP runs cooler, tolerates full-depth cycling, and lasts more cycles, which is why it dominates stationary storage. Older nickel-based (NMC) packs are more energy-dense but run hotter. For a home battery, LFP’s longevity and safety usually make it the right default.
Compare usable (not nameplate) capacity and continuous output in kW, a battery with plenty of kWh but low kW output can’t start a big surge load like an AC compressor.
Is a home battery worth it?
It depends on your goal. For frequent, long outages a battery beats a gas generator on noise, maintenance, and fumes. For time-of-use arbitrage or solar self-consumption, the payback depends on your rate gap. If outages are rare and your rates are flat, the value is mostly resilience, and a smaller essentials battery or a portable generator may be the better buy.
Common questions
How many kWh of battery do you need to back up a house?+−
Essentials-only backup usually needs about 10–20 kWh; whole-home backup often needs 20–40+ kWh. Size it from the appliances you want to run and how many hours of outage you want to cover.
Can a home battery back up my house without solar?+−
Yes. A grid-charged battery stores electricity when the grid is up and discharges during an outage. Without solar it cannot recharge mid-outage, so its runtime is fixed by its capacity and your load.
Is a home battery worth it?+−
It depends on your goal, backup, time-of-use arbitrage, or solar self-consumption. Payback is strongest where outages are frequent or on-peak rates are high; otherwise the value is mostly resilience, not savings.