Home Battery Backup vs Generator

The short version

Pick a battery if your outages are short and frequent, you have rooftop solar or plan to, and you want backup that happens without you lifting a finger. Pick a generator if outages run for days, you're on a well, or you need to run big loads like central air, an electric range and a well pump together. Plenty of homes end up with a small battery for the fridge and lights and a portable generator for the long ones.

Battery vs generator, side by side

The cost figures are HomeGuide's, and battery prices especially move fast, so treat them as a starting range and get quotes.

How much a battery actually covers

This is where most people get surprised. The average US home bought about 899 kWh of electricity a month in 2022, roughly 30 kWh a day. HomeGuide lists one Powerwall at 13.5 kWh of usable storage. So one battery holds well under half a day of average use, and HomeGuide says a home using 25 to 30 kWh a day needs at least two Powerwalls to get through a full day.

There's a second limit besides storage: how much power the battery can push at once. HomeGuide's spec table lists the Powerwall it priced at 5.8 kW continuous. That's plenty for a fridge, lights, internet and a furnace blower, but motors with big starting surges (a well pump, a central AC compressor) can trip a battery that's sized for storage rather than surge. If you're on a well, ask the installer to confirm in writing that the system will start your pump.

In practice a battery works best on a short list of essential circuits, often in a separate backup subpanel. Whole-home battery backup systems exist, but they mean stacking several units.

Home battery backup without solar

You don't need solar panels to own a battery. It can charge from the grid and sit full until an outage. Without solar, though, it can't refill itself during a long outage, so it becomes a fixed tank of energy. With solar, a sunny day can put back some of what you used overnight, which is how battery owners stretch through multi-day outages.

Solar generators and portable power stations

A "solar generator" is a portable battery pack with a built-in inverter and a solar charge input. A portable power station is the same thing, often sold without panels. They're good for camping, a fridge, a CPAP or charging phones. They're not a whole house solar generator in the sense most ads suggest, because their storage is small next to a house's daily use.

Some can tie into a house through a transfer switch or an interlock and inlet box, like a portable generator. Interlock Technologies, for one, describes its kits as being for a secondary source like a portable generator or a solar battery. If you go that route, the power station's output has to match the inlet and cord, and an electrician should confirm it.

Battery backup for gas and tankless water heaters

Gas tankless water heaters need electricity for the controls and fan, so they stop in an outage even with gas flowing. A small battery backup made for tankless units, or a power station on a dedicated outlet, can keep one running for showers. Check the water heater manual for its power draw and whether the maker approves a battery backup and what kind of backup power source it accepts. Most standard tank gas water heaters with a standing pilot don't need power at all.

Small battery boxes also make sense for a home alarm system, a gas boiler's circulator and controls, or a sump pump. For sump pumps, see our sump pump backup page.

When a generator is the better call

• Your outages run for days, especially from ice storms or hurricanes.
• You're on a well. No power means no water, and the pump's startup surge is easier for a generator.
• You want to run central air or electric heat.
• You want backup for well under the cost of a battery system. A portable generator plus an interlock kit is the cheapest safe whole-panel setup.

Standby generators come on automatically, like a battery, and HomeGuide says natural gas units cost the least to run of the fuel types it compared. See our standby generator guide and the generator sizing page to size one.

What to skip

Skip any battery quote that doesn't say which circuits it backs up and whether it will start your biggest motor. Skip "whole house solar generator" kits that hold less than a day of your actual use but are marketed as house backup. And skip any setup that connects to the house without a transfer switch or interlock. Backfeeding is how line workers get hurt.

Install notes

Both systems need permits. A battery install usually adds a backup gateway or transfer device and sometimes a critical-loads subpanel. A standby generator needs a pad, a fuel line and an automatic transfer switch. A portable generator needs an inlet box outside and an interlock or manual transfer switch inside. Batteries carry a long warranty; HomeGuide says Tesla covers the Powerwall for 10 years and guarantees at least 70% of capacity at that point.