Loading NuWatt Energy...
We use your location to provide localized solar offers and incentives.
We serve MA, NH, CT, RI, ME, VT, NJ, PA, and TX
Loading NuWatt Energy...
NuWatt designs, installs, and manages solar, battery, heat pump, and EV charger systems across 9 states. One company, one warranty, one point of contact.
Get a Free QuoteHow long will a home battery power your appliances during an outage? Complete runtime tables for 10 kWh, 13.5 kWh (Powerwall), and 20 kWh batteries with 18 common household appliances.
Quick Answer
A 13.5 kWh Tesla Powerwall will power essential loads (refrigerator, lights, WiFi, phones) for 41+ hours. Adding a furnace blower and TV brings that down to about 13 hours. High-draw appliances like space heaters (1,500W) or window AC (1,200W) drain a single battery in 7-11 hours. For most outages, one battery covers essentials for 1-2 full days.
10 kWh
Enphase IQ Battery 10
9.5 kWh usable
13.5 kWh
Tesla Powerwall 3
12.8 kWh usable
20 kWh
Franklin aPower2 / sonnenCore+
19 kWh usable
Usable capacity accounts for ~5% round-trip inverter losses. Actual performance varies with temperature, battery age, and discharge rate.
Runtime assumes the appliance is the only load drawing from the battery. In practice, you will run multiple appliances simultaneously — see the scenario tables below for realistic combined runtimes.
| Appliance | Watts | Daily Hours | Daily kWh | 10 kWh | 13.5 kWh | 20 kWh |
|---|---|---|---|---|---|---|
| Refrigerator | 150W | 8h | 1.2 | 63.3h | 85.3h | 126.7h |
| Chest Freezer | 100W | 6h | 0.6 | 95h | 128h | 190h |
| Sump Pump | 800W | 0.5h | 0.4 | 11.9h | 16h | 23.8h |
| Well Pump | 1000W | 1h | 1 | 9.5h | 12.8h | 19h |
| Furnace Blower | 500W | 12h | 6 | 19h | 25.6h | 38h |
| CPAP Machine | 60W | 8h | 0.48 | 158.3h | 213.3h | 316.7h |
| Oxygen Concentrator | 300W | 24h | 7.2 | 31.7h | 42.7h | 63.3h |
| WiFi Router + Modem | 20W | 24h | 0.48 | 475h | 640h | 950h |
| Phone Charger | 25W | 3h | 0.075 | 380h | 512h | 760h |
| Security System | 15W | 24h | 0.36 | 633.3h | 853.3h | 1266.7h |
| LED Lights (10 bulbs) | 100W | 6h | 0.6 | 95h | 128h | 190h |
| Garage Door Opener | 550W | 0.1h | 0.055 | 17.3h | 23.3h | 34.5h |
| Appliance | Watts | Daily Hours | Daily kWh | 10 kWh | 13.5 kWh | 20 kWh |
|---|---|---|---|---|---|---|
| Television (55") | 80W | 5h | 0.4 | 118.8h | 160h | 237.5h |
| Laptop Computer | 65W | 8h | 0.52 | 146.2h | 196.9h | 292.3h |
| Appliance | Watts | Daily Hours | Daily kWh | 10 kWh | 13.5 kWh | 20 kWh |
|---|---|---|---|---|---|---|
| Window AC Unit | 1,200W | 8h | 9.6 | 7.9h | 10.7h | 15.8h |
| Space Heater | 1,500W | 8h | 12 | 6.3h | 8.5h | 12.7h |
| EV Charger (Level 1) | 1,400W | 8h | 11.2 | 6.8h | 9.1h | 13.6h |
| EV Charger (Level 2) | 7,600W | 4h | 30.4 | 1.3h | 1.7h | 2.5h |
Runtime = usable battery capacity / appliance wattage. Actual runtime may be 5-15% lower depending on inverter efficiency, battery age, and temperature. Wattage values are typical averages — check your appliance nameplate for exact ratings.
In a real outage, you run multiple appliances simultaneously. These scenarios show realistic combined runtimes based on how people actually use backup power.
| Scenario | Total Watts | Daily kWh | 10 kWh | 13.5 kWh | 20 kWh |
|---|---|---|---|---|---|
| Essential Loads Only | 310W | 2.7 | 30.6h | 41.3h | 61.3h |
| Essential + Medical | 670W | 10.4 | 14.2h | 19.1h | 28.4h |
| Comfort Loads | 955W | 9.7 | 9.9h | 13.4h | 19.9h |
| Full Home (No HVAC) | 2,405W | 11.3 | 3.9h | 5.3h | 7.9h |
Fridge, lights, WiFi, phones, security — the minimum to keep your home safe and connected.
Includes: Refrigerator, LED Lights (10 bulbs), WiFi Router + Modem, Phone Charger, Security System
Essential loads plus CPAP and/or oxygen concentrator. Critical for medically dependent households.
Includes: Refrigerator, LED Lights (10 bulbs), WiFi Router + Modem, Phone Charger, Security System, CPAP Machine, Oxygen Concentrator
Essential loads plus TV, laptop, furnace blower — maintain comfort without luxury.
Includes: Refrigerator, LED Lights (10 bulbs), WiFi Router + Modem, Phone Charger, Security System, Television (55"), Laptop Computer, Furnace Blower
Everything except space conditioning and EV charging. Realistic for moderate-length outages.
Includes: Refrigerator, Chest Freezer, LED Lights (10 bulbs), WiFi Router + Modem, Phone Charger, Security System, Television (55"), Laptop Computer, Furnace Blower, Garage Door Opener, Sump Pump
A single 13.5 kWh battery keeps your refrigerator, lights, WiFi, and phones running for 40+ hours. For most power outages (4-8 hours), one battery is sufficient for essential loads.
Space heaters (1,500W) and window AC (1,200W) drain batteries fastest. A furnace blower (500W) is manageable. For full HVAC backup, plan for 2-3 batteries or pair with solar.
CPAP machines (60W) use almost nothing — 213 hours on a Powerwall. Oxygen concentrators (300W) are more demanding at 42 hours. Both are easily covered by one battery.
A solar array recharges the battery during daylight. An 8 kW solar system produces 25-40 kWh/day, fully recharging a 13.5 kWh battery and powering your home simultaneously during grid outages.
A Tesla Powerwall 3 has 13.5 kWh of usable capacity. Running essential loads only (refrigerator, lights, WiFi, phone charging, security), it lasts 41+ hours. With comfort loads (adding TV, laptop, furnace blower), expect 13-14 hours. Running high-draw appliances like space heaters or AC, battery life drops to 7-9 hours.
A 10 kWh battery (like the Enphase IQ Battery 10) powers essential loads for about 30 hours. For comfort loads including a furnace blower, expect 10 hours. A single high-draw appliance like a space heater (1,500W) drains a 10 kWh battery in about 6.3 hours.
A single battery (10-13.5 kWh) can run a window AC unit (1,200W) for 7.9-10.7 hours. A central AC system (3,500-5,000W) would drain even a 20 kWh battery in 3-5 hours. For reliable AC backup, you need 2+ batteries or solar paired with battery to recharge during the day.
Yes. A well pump draws about 1,000W while running but only operates 1-2 hours per day. A 10 kWh battery can power a well pump for 9.5 hours of continuous pumping. Since well pumps cycle on and off, one battery provides multiple days of water access during an outage.
Level 1 EV charging (120V, 1,400W) is feasible: a 13.5 kWh battery provides about 9 hours of charging, adding roughly 36 miles of range. Level 2 charging (240V, 7,600W) is not practical — it drains a 13.5 kWh battery in under 2 hours, adding only about 16 miles of range.
Lithium-ion batteries lose 10-15% capacity in freezing temperatures. A 13.5 kWh Powerwall might deliver only 11.5-12.2 kWh at 20 degrees F. Most modern batteries have built-in thermal management, but garage or outdoor installations in northern states should account for winter capacity loss.
Use our battery backup planner to build your custom load profile and find the right battery size for your home.