The average U.S. home uses about 28 kWh a day (865 kWh a month, EIA). Backing up all of it for a full day takes about two 13.5 kWh batteries.
How it works
Energy = average load × hours. Batteries = the larger of energy ÷ usable kWh per battery and peak load ÷ kW per battery, rounded up.
Example: 28.8 kWh of backup with a 10 kW peak needs 3 × 13.5 kWh batteries, about $46,941 installed.
At a glance
Same settings as the calculator, changing only the hours.
| Hours | Energy | Batteries | Cost |
|---|---|---|---|
| 8 h | 9.6 kWh | 1 | $15,647 |
| 12 h | 14.4 kWh | 2 | $31,294 |
| 24 h | 28.8 kWh | 3 | $46,941 |
| 48 h | 57.6 kWh | 5 | $78,235 |
| 72 h | 86.4 kWh | 7 | $109,529 |
Tesla Powerwall 3 at a glance
| Usable energy | 13.5 kWh |
|---|---|
| Continuous power | 11.5 kW |
| Off-grid continuous power with solar | up to 15.4 kW |
| Charging power | 5 kW |
| Average installed cost (13.5 kWh battery, EnergySage, H1 2026) | $15,647 |
Common questions
How many batteries do I need for a whole house?
The average home uses about 28 kWh a day. Two 13.5 kWh batteries cover a full day only if you trim heavy loads; essentials-only backup often needs one.
How much does a home battery cost?
EnergySage puts a 13.5 kWh battery at $15,647 installed on average in the first half of 2026, before incentives.
Is there a tax credit for batteries?
The 30% Residential Clean Energy Credit also covered batteries, but it ended for installations after December 31, 2025.
Sources
- Tesla, Powerwall 3 specifications: https://service.tesla.com/docs/Public/Energy/Powerwall/Powerwall-3-with-Gateway-3-Installation-Manual-NA-EN/GUID-EC527BC7-4750-4425-BBC4-DB8C000339B3.html
- EnergySage, Solar battery backup cost (H1 2026): https://www.energysage.com/energy-storage/solar-battery-backup/
- U.S. EIA, Today in Energy: average residential use 865 kWh a month in 2024: https://www.eia.gov/todayinenergy/detail.php?id=65244