How Long Will a 10 kWh Battery Last in a Power Outage?

Short answer: a 10 kWh home battery runs the essentials (a fridge, internet, lights, phone charging and a few small loads, about 300 to 500 W on average) for roughly 19 to 32 hours. Running a typical US home's average load of about 1,200 W, it lasts about 8 hours. With solar panels recharging it each day, it can keep essentials going indefinitely in sunny weather.

Try your own appliances and battery in the battery runtime calculator.

The formula

hours = usable kWh × (1 − reserve) × efficiency × 1,000 ÷ average load in watts

Home batteries are sold by usable capacity, but you lose a few percent converting stored DC power into household AC, and most systems keep a backup reserve you set in the app (often 20%) so there is always something left when the grid goes down. This guide assumes 95% efficiency, because home battery ratings already allow for most inverter losses.

How long a 10 kWh battery lasts

Average load is not the same as the highest load: a fridge draws about 150 W while its compressor runs but averages 50 to 70 W across a day. The average is what decides how long the battery lasts. Your highest load at any moment has to fit within the battery's power rating (kW), or it will shut off.

How long does a Powerwall last?

A Tesla Powerwall 3 stores 13.5 kWh, so it lasts about 35% longer than a 10 kWh battery: about 26 hours at 500 W and 13 hours at 1,000 W from full. Two Powerwalls double that. In the UK, where the average home uses only about 310 W, a 10 kWh battery covers about a day of normal use.

"How long does a Powerwall last" can also mean its lifespan. Tesla's warranty runs 10 years with a guaranteed share of capacity left at the end; FranklinWH and Enphase offer 15 years. Lithium iron phosphate (LFP) home batteries are typically rated for thousands of full cycles, so age rather than use is usually what ends their life.

Adding solar changes everything

A 5 kW solar array with 4.5 peak sun hours makes about 18 kWh on an average day, more than enough to refill a 10 kWh battery and run essentials during daylight. During a multi-day outage, that turns a one-day battery into an indefinite one in good weather. In winter or a storm, solar can fall to a fraction of that, so plan for the battery alone to cover the first night.

Many solar inverters shut down in a power cut unless they are paired with a battery and a backup gateway or transfer switch, so check how your system is wired.

Making a battery last longer in an outage

• Switch off big heating and cooling loads. Electric heat, central air and water heaters use more in an hour than a fridge does in a day.
• Use a gas stove or a microwave rather than an electric oven or range.
• Keep the fridge and freezer closed; they stay cold for hours without power.
• Set a higher backup reserve before storm season, so the battery is fuller when the grid fails.
• Back up only essential circuits with a critical-loads panel, so heavy appliances cannot drain the battery by accident.

Frequently asked questions

Can a 10 kWh battery run a house?

For essentials, yes, for about a day. For a whole house with air conditioning or electric heat, only for a few hours; the average US home uses about 28 kWh a day.

How long will a 10 kWh battery run a refrigerator?

A modern fridge uses about 1.2 to 1.6 kWh a day, so a 10 kWh battery could run a fridge alone for six days or more. See how much electricity a fridge uses.

How many kWh battery do I need for a power outage?

Add up what you want to run and for how long. The home battery size calculator does this and shows how many batteries cover both the energy and the power.

Sources

• Battery capacities and warranties from manufacturer specifications (Tesla Powerwall 3, FranklinWH aPower 2, Enphase IQ Battery 5P), checked October 2026.
• US Energy Information Administration, average US household electricity use.
• Ofgem, average gas and electricity use.

Checked October 22, 2026.