- Solar is optional. A grid-charged battery provides the same outage protection, limited to the energy it stored.
- It is a resilience purchase. Bill savings without solar are usually too small to pay the system back.
- Size it for power as well as energy. The battery must be able to run and start your loads, not only last long enough.
Find the size your own loads need.
Open the Battery Size Calculator →How it works
The battery charges from the grid. When the grid fails, the system isolates your home from the utility and powers the backed-up circuits from stored energy, quickly enough that most electronics do not notice. When the grid returns it reconnects and recharges.
Which circuits are backed up is decided at installation. Some systems back up the whole panel; many back up a set of essential circuits to keep the battery from being drained by a large appliance.
What one battery can and cannot do
Two numbers on the spec sheet matter:
- Usable energy (kWh) sets how long it lasts.
- Continuous output (kW) sets what it can run at one moment. Starting capability, published as a surge rating or as LRA, sets whether it can start motors.
Current products differ widely on the second number. Among units whose manufacturer documents we checked, continuous output per unit ranges from under 4 kW to 11.5 kW, and usable energy from 5 to 15 kWh. The full list, with sources and dates, is on our assumptions and sources page.
In practice a single battery comfortably runs essentials. Central air conditioning is the common sticking point: it uses a lot of energy and its compressor needs a starting surge that some single-unit systems cannot supply without a soft-start device.
Sizing without solar
- List what must stay on. Refrigerator, some lights, internet, phone charging, medical equipment, a well or sump pump if you have one.
- Add up energy per day. The Outage Simulator does this with editable wattages.
- Choose how long. With no solar there is no recharge, so outage length multiplies directly. Essentials for twelve hours is a small battery. Essentials for three days is two or three. Whole-home for three days is not realistic on batteries alone.
- Check power. Make sure the continuous and starting ratings cover what runs at once.
If the answer comes out at several batteries, compare a generator or a battery plus a generator before going further.
What it costs
Our planning range for a professionally installed home battery is about $1,000 to $1,400 per kWh, so roughly $14,000 to $19,000 for a 13.5 kWh unit, before any state or utility incentive. Electrical work, a backup panel, and site conditions move the number. No federal residential tax credit applies to systems installed after 2025.
Can it pay for itself?
Without solar there are two sources of savings:
- Time-of-use shifting. Charge when power is cheap, use it when power is expensive. The value is the price gap times the energy you actually cycle. A 10-cent gap on 10 kWh a day is about $365 a year in an ideal case, and less in practice.
- Grid programs. Some utilities and retail providers pay battery owners to discharge during peak events. Availability and payment vary widely.
Against an installed cost in the mid five figures, those amounts rarely recover the purchase within the battery's warranty period. It is more accurate to treat a standalone battery as insurance against outages, and to count any savings as a partial offset.
Practical points
- Heat. Batteries have operating temperature limits and may reduce output in extreme heat. Follow the manufacturer's siting guidance.
- Permits and notification. Expect an electrical permit, and in many areas a notice or application to the utility, even without solar.
- Adding solar later. Some batteries include a solar inverter and some do not. If solar is likely, ask now what adding it would involve.
- Generator charging. If you might add a generator, confirm the battery supports it.
Common questions
Yes. A battery can charge from the grid and back up your home in an outage exactly as a solar-paired one does. The difference is that with no solar it cannot recharge until the grid returns, so its runtime is limited to what it stored.
Not for new installations. From 2023 through 2025 the Residential Clean Energy Credit covered standalone battery storage. It does not apply to systems placed in service after December 31, 2025. Some states, utilities and retail electricity providers offer rebates or pay for battery participation in grid programs.
It depends on what you leave on. Essentials such as a refrigerator, lights, internet and a few outlets often use 4 to 8 kWh a day, which one 13.5 kWh battery can carry for a day or more. Add central air and the same battery may last a few hours.
Rarely on bill savings alone. Without solar the only savings come from time-of-use rate differences or grid-program payments, which are usually small against the installed cost. Most people who buy one are paying for backup, and should judge it on that.