How many 100Ah batteries to power a house?
A full day of an average US home (28.4 kWh, EIA 2024) takes about 31.6 kWh of usable battery — 31 batteries of 12 V 100Ah LiFePO4 at 80% usable, or 8 modules of 48 V 100Ah.
How to work it out
- 28.4 kWh a day × 100% × 24 h ÷ 24 = 28.4 kWh of use
- ÷ 90% inverter = 31.6 kWh usable battery → 4 units of 10 kWh
- or 31 batteries (1.024 kWh usable each) · 8 modules (4.096 kWh usable each)
A 12 V 100Ah LiFePO4 battery holds 1.28 kWh, of which about 1.02 kWh is usable at 80%. That is a useful size for vans and small backup kits, but a whole house quickly runs to dozens of them.
Adjust for your project
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- Battery units
- 4 units
- 12 V 100 Ah LiFePO4 batteries (at 80% usable)
- 31 batteries
- 48 V 100 Ah LiFePO4 modules (at 80% usable)
- 8 modules
- Average load during the outage
- 1,183 W
- Backing up a whole house takes a large battery. Many outage plans cover essentials only — fridge and freezer, lights, internet, the furnace fan or well pump — and let the big heating, cooling and cooking loads wait.
- Battery size covers how long; the inverter’s continuous and surge rating covers what can run at once — a well pump or central air needs a much bigger inverter than lights and a fridge.
Battery needed for longer outages
| Outage to cover | Usable battery needed | Battery units | 48 V 100 Ah LiFePO4 modules (at 80% usable) |
|---|---|---|---|
| 4 | 5.3 kWh | 1 unit | 2 modules |
| 8 | 10.5 kWh | 2 units | 3 modules |
| 12 | 15.8 kWh | 2 units | 4 modules |
| 24 | 31.6 kWh | 4 units | 8 modules |
| 48 | 63.1 kWh | 7 units | 16 modules |
| 72 | 94.7 kWh | 10 units | 24 modules |
What to know about building a house battery from 100 Ah batteries
- Wire them as 48 V. Four 12.8 V batteries in series make a 51.2 V string; a house-sized bank is several of those strings in parallel. Check the battery maker’s limit on series and parallel connections.
- Lead-acid doubles the count. At 50% usable, a 12 V 100Ah lead-acid battery gives about 0.6 kWh, so the same day takes about 53 of them — and weighs roughly twice as much per battery.
- Essentials take far fewer. The calculator’s essentials list — fridge, freezer, lights, internet, charging, furnace fan — needs about 7.5 kWh for a day: eight 12 V 100Ah LiFePO4 batteries.
- Purpose-built 48 V modules are simpler. A 51.2 V 100Ah module replaces four 12 V batteries with one box and one set of connections.
The energy in each battery is on how many watt-hours in a 100Ah battery, and a full off-grid version of the same house on an off-grid solar system for a house. The day’s kWh is worked through on how many kWh to power a house for a day.
Different size? Use the full Home Backup Battery Calculator.
What you’ll need
- 12 V 100 Ah LiFePO4 batteryPremium price
About 1.28 kWh rated in a box roughly the size of a group 24–31 lead-acid battery at around half the weight. Check the BMS discharge limit and whether it can charge below freezing.
See options on Amazon (opens in a new tab) - Battery monitor with shuntMid-range price
Counts amp-hours in and out, so you see true state of charge instead of guessing from voltage — which barely moves on a LiFePO4 battery until it is nearly empty.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How many 100Ah batteries to run house essentials for a day?
About 8 batteries of 12 V 100Ah LiFePO4 (7.5 kWh usable).
How many 100Ah batteries to power a house for 12 hours?
About 16 batteries of 12 V 100Ah LiFePO4, or 4 modules of 48 V.
Other common sizes
- How many kWh to power a house for a day — 28.4 kWh a day — about 31.6 kWh of battery
Sources
- U.S. Energy Information Administration — Electric Sales, Revenue, and Average Price, Table 5A (2024 data, released October 2025) (opens in a new tab) — 2024 average residential customer: 863 kWh a month (about 10,359 kWh a year, 28.4 kWh a day); Louisiana 1,202 kWh a month, Hawaii 495.
- Champion Power Equipment — Generator Wattage Chart (opens in a new tab) — Typical running and starting watts for household, RV and job-site appliances (a manufacturer’s planning chart — your nameplate wins).
- Victron Energy — Lithium Battery Smart manual, technical data (opens in a new tab) — LiFePO4 12.8 V: cycle life 2,500 at 80% DoD, 3,000 at 70%, 5,000 at 50% (to 80% of capacity); 92% round-trip efficiency; 12.8 V 100 Ah: recommended continuous discharge ≤100 A (1C), maximum 200 A; capacity about 20% lower at 0 °C; charge only between +5 °C and +50 °C.
- Victron Energy — Energy Unlimited (book) (opens in a new tab) — Lead-acid charge efficiency 80–95% (85% suggested as a starting value); battery energy efficiency about 75% for full cycles, about 89% in partial state of charge; inverter efficiencies above 90%.
- OSHA Fact Sheet — Using Portable Generators Safely (opens in a new tab) — Never attach a generator to a building’s wiring unless a qualified electrician has installed a transfer switch; 3–4 ft of clear space around the unit.
- U.S. Consumer Product Safety Commission — Portable Generator Hazards (Safety Alert 5123, 2021) (opens in a new tab) — Never run a generator indoors or in a garage, even with doors open; place it outside far from doors, windows and vents; CO alarms; never “backfeed” by plugging into a wall outlet.