How many batteries to power a house depends on two numbers, not one. Energy (kWh) decides how long you last. Power (kW) decides what you can run at the same time, including the startup surge of an AC or well pump. Most homes run out of power capacity before they run out of energy.
Electrical work can be dangerous: follow the manual, fuse and size every cable correctly, and use a licensed electrician for anything connected to household wiring.
Step 1: Find Your Daily Use
Your bill or utility app shows kWh per day. The US average is roughly 29 kWh/day (EIA, about 860 kWh a month in recent years), but yours could be half or double that.
Step 2: Decide What to Back Up
- Essentials: fridge, Wi-Fi, lights, furnace blower, phones. Often 5–10 kWh a day.
- Partial home: add a well pump, a microwave, some outlets. Often 10–20 kWh a day.
- Whole home: central AC, electric range, dryer. Can be 30+ kWh a day.
Step 3: Check Peak Power and Surge
Add the running watts of everything that could run at the same time, then the biggest startup surge. A 3-ton central AC can pull 80–120A at startup (locked-rotor amps). The battery’s continuous kW and its motor-starting rating have to cover it.
How Many Batteries to Power a House: Examples
Illustrative, using common unit sizes (about 13.5–15 kWh and 10–11.5 kW per unit):
| Goal | Energy for 1 day | Peak need | Units |
|---|---|---|---|
| Essentials | ~8 kWh | ~3 kW | 1 |
| Partial home | ~15 kWh | ~6 kW | 1–2 |
| Whole home with AC | ~30 kWh | ~10–14 kW | 2–3 |
Add solar and the battery refills each sunny day, so you need less stored energy for long outages.
Ways to Need Fewer Batteries
- Load management: smart panels or load controllers shed big loads automatically.
- Soft starters on AC compressors cut startup surge.
- Critical loads panel: back up only selected circuits.
- Generator support: some systems recharge from a generator.
Step 4: Build a Load List (Worked Example)
DOE’s “Estimating Appliance and Home Electronic Energy Use” guide gives the method: watts × hours used per day ÷ 1,000 = kWh per day. Check each appliance’s label for its actual watts. Here’s an example essentials-plus list (illustrative wattages and hours):
| Load | Running watts | Hours/ | kWh/ |
|---|---|---|---|
| Refrigerator (cycling) | 150 average | 24 | 3.6 |
| Furnace blower | 500 | 8 | 4.0 |
| Lights (LED) | 100 | 6 | 0.6 |
| Wi-Fi, modem, laptop | 80 | 12 | 1.0 |
| Microwave | 1,200 | 0.25 | 0.3 |
| Well pump | 1,000 | 1 | 1.0 |
| TV | 100 | 4 | 0.4 |
| Total | 10.9 kWh/ |
That home needs about 11 kWh a day. One 13.5 kWh battery covers about a day with no solar, with some margin for losses. For appliance-specific numbers, see how many watts a refrigerator uses and how to read an appliance label.
Step 5: Add Up Simultaneous Power
Energy isn’t the only limit. Add up what could run at the same moment:
- Well pump 1,000 W + microwave 1,200 W + furnace blower 500 W + fridge compressor running about 150 W + lights and electronics 280 W = 3,130 W
- Add the largest motor’s startup surge. A well pump can briefly draw several times its running watts.
A battery rated 5 kW continuous covers 3.1 kW comfortably. Enphase’s IQ Battery 5P (3.84 kW continuous per unit) would need two units for headroom. Read more in surge watts vs running watts.
Battery Units Compared by the Numbers
| Battery | Usable kWh per unit | Continuous kW per unit | Units for 30 kWh | kW with that many units |
|---|---|---|---|---|
| Tesla Powerwall 3 | 13.5 | 11.5 | 3 (or 1 + 2 Expansions) | 34.5 (or 11.5 with Expansions) |
| FranklinWH aPower 2 | 15 | 10 | 2 | 20 |
| Enphase IQ Battery 5P | 5.0 | 3.84 | 6 | 23 |
Specs from each maker’s datasheet. Expansions add energy, not power. Real system limits also depend on the gateway and inverter. See Powerwall 3 vs Enphase vs FranklinWH.
Worked Example: Multi-Day Outage With Solar
A home uses 15 kWh a day on backup, with a 27 kWh battery bank and 7 kW of solar:
| Day | Weather | Solar made (example) | Battery at end of day |
|---|---|---|---|
| Start | 27 kWh | ||
| 1 | Sunny | 28 kWh | 27 kWh (full, extra unused) |
| 2 | Cloudy | 8 kWh | 20 kWh |
| 3 | Cloudy | 6 kWh | 11 kWh |
| 4 | Sunny | 28 kWh | 24 kWh |
With solar, the battery only has to bridge bad-weather days, not the whole outage. Without solar, the same 27 kWh lasts under two days. Our guide on home battery backup without solar covers that case.
Battery Size in Amp-Hours vs kWh
Home batteries are rated in kWh, but DIY and RV batteries are often rated in amp-hours (Ah). Convert with: kWh = volts × Ah ÷ 1,000.
| Battery | Math | Energy |
|---|---|---|
| 12 V 100 Ah | 12.8 × 100 ÷ 1,000 | about 1.28 kWh |
| 48 V 100 Ah | 51.2 × 100 ÷ 1,000 | about 5.12 kWh |
| 48 V 280 Ah | 51.2 × 280 ÷ 1,000 | about 14.3 kWh |
LiFePO4 batteries use a nominal 3.2 V per cell, so “12 V” and “48 V” packs are 12.8 V and 51.2 V nominal. A 13.5 kWh home battery equals roughly ten 12 V 100 Ah batteries. More in amp-hours vs watt-hours.
Step-by-Step: Sizing Summary
- Get kWh per day from your bill or utility app.
- Choose essentials, partial or whole home.
- List loads, watts and hours, and total the kWh.
- Add simultaneous watts plus the largest motor surge.
- Pick units that meet both energy and power.
- Decide hours or days of backup, and whether solar will recharge.
- Consider a critical loads panel or load management to need fewer batteries.
Heating and Cooling: The Biggest Variable
Central AC and electric heat often decide how many batteries a house needs. A 3 kW AC running half the time uses 1.5 kW × 24 = 36 kWh a day by itself. Gas heat with an electric blower uses far less battery than a heat pump or electric furnace in winter. If you want AC on backup, size the power for its starting surge and the energy for its running hours, or plan to run it only part of the day.
FAQ
Can one battery power a whole house?
For a few hours, maybe, if loads are managed. Most whole-home setups with central AC use two or more.
How long will a 13.5 kWh battery last?
About 13.5 ÷ your average kW. At a 1 kW average, around 12 hours, minus some losses.
Do I need solar with a home battery?
No, but without solar the battery can’t refill during a long outage.
How many batteries do I need to power my house for 24 hours?
Divide your daily kWh by each battery’s usable kWh. At the U.S. average of about 29 kWh a day, that’s 2 to 3 units of 13.5 to 15 kWh, before losses.
How many Powerwalls do I need for a 2,000 sq ft house?
Square footage doesn’t decide it. Daily kWh and peak load do. Many homes of that size use 20 to 40 kWh a day, which means 2 to 3 Powerwall-size batteries for full-day whole-home backup.
Can I power my AC with a home battery?
Yes, if the battery’s continuous power and surge rating cover the compressor. Plan for its energy use too: a 3 kW unit running half the time uses about 36 kWh a day.
Sources: U.S. Department of Energy, “Homeowner’s Guide to Going Solar” and “Estimating Appliance and Home Electronic Energy Use”; EIA residential consumption FAQ; manufacturer datasheets; Tesla Powerwall 3, FranklinWH aPower 2 and Enphase IQ Battery 5P datasheets. Accessed Oct 2026.
Related: Jackery HomePower 3600 Plus: What Can It Power?, EcoFlow Delta 3 Max for Home Backup
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