Home Battery Backup: What It Powers, How Long It Lasts and What It Costs in 2026

Home battery backup keeps selected lights, outlets and appliances running when the grid goes down. A typical 13.5 kWh battery can carry a refrigerator, internet, lights and phone chargers for most of a day, and much longer if solar panels recharge it. Whole-home backup with air conditioning usually takes two or three batteries.

This guide covers what a battery can and cannot run, how to size one, how it compares with a generator, the safety codes that apply and what changed for costs and credits in 2026.

Why don't solar panels alone keep the power on?

Grid-tied solar panels switch off automatically when the grid fails, so they will not send power onto lines that crews are repairing. The U.S. Department of Energy explains that keeping power on requires an inverter and a storage system that can island your home, meaning disconnect it from the grid and run it separately.

That surprises many owners after their first outage. The panels on the roof may be in full sun, yet the house is dark. DOE's Solar and Resilience Basics (opens in a new tab) page notes that solar generally depends on the grid to operate and is designed to shut off when grid power is cut.

A backup-ready system has three parts:

1. A battery that stores energy for use when the grid is down.
2. A backup-capable inverter (sometimes built into the battery) that can form its own small grid for your home.
3. An automatic transfer switch or gateway that disconnects your home from the utility within moments of an outage and reconnects it when power returns.

How common is home battery backup now?

Batteries have gone from a niche add-on to a common part of new solar systems. Lawrence Berkeley National Laboratory reports that 37% of new U.S. residential solar systems in 2025 were paired with storage, up from 25% in 2024, with the largest jumps in California, Arizona and Texas.

The same Berkeley Lab 2026 data update (opens in a new tab) (August 2026) found the median residential battery paired with solar held 13.5 kWh in 2025, about the same as a year earlier. That is why our examples use 13.5 kWh. Power output per unit rose sharply, so newer batteries can start larger loads such as well pumps and air conditioners more easily.

Outages are also getting longer in some regions. The U.S. Energy Information Administration reports (opens in a new tab) that customers averaged about 11 hours without power in 2024, nearly twice the average of the decade before, mostly because of Hurricanes Beryl, Helene and Milton. South Carolina customers averaged nearly 53 hours. Homeowners in hurricane and ice-storm areas, such as those reading our guide to solar panels in Florida or Texas, feel this most.

How long will a home battery last in an outage?

A full 13.5 kWh battery running an average load of 800 watts lasts about 13.7 hours with no solar recharge, assuming a 10% reserve and 90% inverter efficiency. Runtime depends almost entirely on how much power you draw, so trimming your load is the cheapest way to make backup last longer.

Here is the math behind that figure. Usable energy is 13.5 kWh × (100% − 10% reserve) × 90% efficiency = 10.9 kWh. Divide by the 0.8 kW load and you get 13.7 hours. Try your own numbers below.

Computed with our battery backup runtime calculator using a 10% reserve and 90% inverter efficiency.

Note the third row. Many owners let the battery cycle daily to save on time-of-use rates, so it may not be full when a storm hits. Most systems let you raise the backup reserve before a forecast storm. Do it.

With solar recharging, the picture changes. On an average day, a 7 kW system with 4.3 peak sun hours makes about 26 kWh, enough to refill one battery and run daytime loads. Cloudy winter days produce far less, so plan for your worst season, not your best.

What can a home battery run, and what can't it?

One battery comfortably runs essential loads: refrigerator, freezer, lights, internet, phone and laptop charging, a TV, a medical device and a gas furnace fan. Large electric loads such as central air, electric ranges, water heaters, dryers and EV chargers drain a single battery in hours and are usually left off the backup circuits.

Sizing starts with daily energy, not panel count. Our solar battery size calculator adds up watts × hours for each item. Using its default essentials (a refrigerator running all day at an average 150 W, LED lights, a router, chargers, a TV and a few minutes of microwave), daily use is 5.7 kWh. After allowing for 90% usable capacity and losses, that calls for about 6.7 kWh of battery, so one 13.5 kWh unit covers a full day with room to spare.

Calculated with the site calculator's default load values; your appliances may differ.

Power matters as well as energy. A well pump or air conditioner pulls a short surge when it starts. If the battery's continuous and surge power ratings are too low, the system can trip even with plenty of stored energy. Ask your installer for the battery's continuous kW and surge rating, and compare them with the nameplates on your largest motors.

Partial-home or whole-home backup: which do you need?

Most homes do best with partial-home backup: a single battery wired to a short list of essential circuits. Whole-home backup covers every circuit but typically needs two or three batteries plus load controls, and it costs much more. Choose based on outage length, climate and medical needs.

There are two common wiring approaches:

• Critical loads panel. The installer moves essential circuits to a separate subpanel that the battery feeds. It is simple and keeps you from accidentally draining the battery, but you cannot use other circuits during an outage.
• Whole-home with load management. The battery backs up the main panel, and smart breakers or load controllers shed big loads (AC, water heater, EV charger) automatically when the battery runs low.

Berkeley Lab research (opens in a new tab) funded by DOE has found that solar plus storage can keep critical loads running through multi-day outages in most of the country, but far fewer homes can run everything, especially homes with electric resistance heat in winter. Heat pumps fared better because they use less energy for the same heat.

Is a battery or a standby generator better for backup?

A standby generator is cheaper per hour of long-outage backup and can run a whole house for days on fuel. A battery is silent, needs little maintenance, recharges from solar and can lower bills on time-of-use rates. Over 10 years, total costs can be close, so your outage pattern decides it.

Using example inputs in our battery vs generator cost calculator ($14,000 battery, $12,000 generator, $250 a year of generator maintenance, 24 outage hours plus 26 hours of self-testing at 1.5 units of fuel per hour and $2.50 per unit), the generator costs $16,375 over 10 years and the battery $14,000. Fuel alone is about $188 a year.

Change the inputs and the gap shifts. If outages last 60 hours a year and the battery also saves $500 a year on time-of-use rates, the battery's 10-year net cost drops to $9,000 while the generator's climbs to $17,725. If you rarely lose power and have no time-of-use rate, neither may pay off, and a portable power station for the fridge could be enough.

For California homes, battery savings under net billing can be large, which we cover in our California NEM 3.0 guide. For whether a battery pays off on bill savings alone, read are solar batteries worth it.

What safety rules apply to home batteries?

Residential batteries must be listed and labeled to UL 9540, the safety standard for energy storage systems, and installed under your local building and fire code. Codes based on NFPA 855 and the International Residential Code limit each unit to 20 kWh and cap total storage in each location.

UL's summary of the 2021 residential requirements (opens in a new tab) (IRC Section R328 and NFPA 855 Chapter 15) lists the key rules:

• Listing: every system listed to UL 9540. Fire test data from UL 9540A can justify closer spacing or larger totals.
• Unit size: no more than 20 kWh per unit.
• Total storage: up to 40 kWh in utility closets, basements and storage spaces; up to 80 kWh in attached or detached garages, on exterior walls or outdoors on the ground.
• Spacing: units at least 3 feet apart unless UL 9540A test data supports less.

States and cities adopt different code editions and amendments, so your local building department has the final word. The NFPA's storage fact sheet (opens in a new tab) (February 2024) points new installations to the 2023 edition of NFPA 855 and notes that a battery management system should monitor the modules and disconnect them when something goes wrong.

What does home battery backup cost in 2026?

Battery prices vary widely by brand, capacity and how much rewiring your panel needs. Berkeley Lab found that cash-purchased residential solar systems with storage had median prices $2.1 per watt higher than solar alone in 2025, which works out to roughly $14,700 extra on a 7 kW system.

That figure comes from the Berkeley Lab 2026 data update (opens in a new tab), and about 80% of its paired pricing data comes from California, so prices elsewhere may differ. Our calculators use $14,000 as a round example. Always get itemized quotes that separate the battery, the backup gateway and any panel upgrade.

The federal credit picture changed this year. As of October 2026, the 30% Residential Clean Energy Credit (Section 25D) no longer applies to a battery you own if its installation was completed after December 31, 2025. The IRS FAQ on the 2025 law changes (opens in a new tab) says the expenditure is treated as made when installation is completed, so paying a deposit in 2025 does not count. Batteries of at least 3 kWh finished in 2025 are claimed on the 2025 return using Form 5695, per the IRS Residential Clean Energy Credit page (opens in a new tab).

If a company owns the battery under a lease or service plan, the owner may still claim a business storage credit under separate rules with a longer timeline. You do not claim it, but it may lower the price you are offered. State and utility battery programs also still exist in some areas; check your utility's website and your state energy office.

How do you plan a home battery backup system?

Plan backup in a few steps: list must-have loads, estimate daily energy and peak power, decide how many days you want covered, then choose partial- or whole-home wiring. Get at least two quotes that show the battery's usable kWh, continuous kW and which circuits are backed up.

1. List your must-run loads, including medical devices, well or sump pumps and the furnace fan.
2. Estimate daily kWh with the battery size calculator and check peak kW against the battery's power rating.
3. Pick your target outage length, using your utility's outage history and your climate.
4. Decide on wiring: critical loads panel or whole-home with load management.
5. Check the code rules for where the battery can go, especially if your only option is a basement or utility closet.
6. Compare quotes on usable kWh, warranty years and throughput, backup circuits and total installed price.
7. Set the backup reserve after installation, and raise it before storms.

A battery is a long-term purchase, so read the warranty for both years and energy throughput, and confirm who services it locally. The DOE Homeowner's Guide to Solar (opens in a new tab) suggests asking your installer directly which storage options they support and how outage backup will work in your home.