Home batteries: what they do, and what they don't
A home battery is a very good way to keep the fridge, the internet and the furnace running through an outage. It is a very expensive way to run central air for a week. Most disappointment comes from confusing the two.
By Aatish Patel, founder of XCharge North America
- What it does
- What it doesn't
- kW and kWh
- Surge
- Essentials or whole home
- Kinds
- Cost and credits
- Or a generator
- Ask the installer
What a home battery does
- Backup. When the grid goes down, a gateway disconnects the house from the street and the battery runs whatever it's wired to. Done properly, you notice a flicker, or nothing.
- Time shifting. Charge when power is cheap, from the grid overnight or from solar at midday, and run the house from the battery through the expensive evening peak.
- Solar self-consumption. Where exporting solar pays little, like California under net billing, storing it for the evening is worth far more than selling it at noon.
- Getting paid. Some utilities and aggregators pay you to let them discharge your battery on a handful of stressed evenings a year. These virtual power plant programs can pay real money. Read the fine print on how much backup they leave you.
What it doesn't do
- Run a big house for days. A single battery holds 10 to 15 kWh. A typical American home uses about 30 kWh a day, far more with air conditioning or electric heat. The math is not on your side.
- Pay for itself on a flat rate. If your price per kWh is the same all day and exports pay fairly, a battery is insurance. That's fine, but call it that.
- Go off-grid. Without solar to refill it, a battery is a very large, very expensive flashlight. It runs down and stays down.
- Start everything at once. Motors need a big kick to start. More on that below, because it's the thing that catches people out.
Kilowatts and kilowatt-hours
Think of a water tank with a tap. The kilowatt-hours are how much water is in the tank. The kilowatts are how wide the tap opens. A battery needs enough of both: the tap has to open wide enough to run everything that's on at the same time, and the tank has to last until the grid comes back or the sun comes up.
Turn things on. Watch the battery.
Surge, the part that catches people out
An air conditioner running at 3 kW can need five or six times that for a split second to start its compressor. Well pumps, sump pumps and fridges do the same on a smaller scale. Electricians call it locked-rotor current, and batteries rate it as surge or peak power. If the battery can't supply that kick, the compressor doesn't start, and the battery may shut down to protect itself.
- Check the battery's surge rating, not only its continuous kW. Some publish a locked-rotor amps number, and 185 amps is roughly the class that starts a typical central air unit.
- A soft starter on the air conditioner, a few hundred dollars installed, cuts the starting kick by half or more. It's often the cheapest way to make a smaller battery work.
- Only one big motor usually starts at a time, so you size for the running load plus the single biggest kick, not the sum of every kick.
Essentials, or the whole home
There are two ways to wire a backup battery. Essentials backup moves the important circuits to a separate panel the battery can always handle: fridge, lights, internet, furnace fan, a few outlets. Whole-home backup puts the battery in front of the entire house, and relies on you, or the system, to not run the dryer, the oven and the air conditioner at once during an outage.
Whole-home is simpler to wire and nicer to live with, but needs more battery. Essentials is cheaper and hard to overload. Some systems split the difference with smart breakers that shed big loads automatically when the grid is down.
The backup sizer works out the running power, the surge and the kilowatt-hours for the things you pick, then lists which batteries cover them and how many you'd need.
The kinds of battery
| What it means | Why you'd care | |
|---|---|---|
| AC coupled | The battery has its own inverter and connects like any other appliance. | Easy to add to an existing solar system. |
| DC coupled, or hybrid | One inverter for the solar and the battery. | More efficient for new solar-plus-battery installs. Harder to mix brands. |
| LFP chemistry | Lithium iron phosphate. | Long life, stable, a bit heavier. Most new home batteries use it. |
| NMC chemistry | Nickel manganese cobalt. | More compact. Common in older units. |
| Portable power stations | Big battery packs on wheels, wired in through a smart panel. | Cheaper per kWh and portable. Shorter warranties, smaller inverters. |
| Battery as a service | A company installs and owns the battery, you pay a fee or buy power from them. | Low upfront cost. You don't own it, and the contract matters more than the hardware. |
What it costs, and what the government pays
Installed prices in 2026 cluster between about $900 and $1,400 per kWh. EnergySage's first-half 2026 median was $15,647 for a 13.5 kWh system, before any incentives. Additional units in the same install usually cost less than the first, because the gateway and the electrician's first day are already paid for.
- The 25D residential credit is gone for new installs. It doesn't apply to systems whose installation was completed after December 31, 2025. Buying in 2025 but installing in 2026 doesn't count.
- Leases and power purchase agreements can still carry a credit. The company that owns the battery may claim the 48E business credit and fold some of it into your price. That's one reason battery-as-a-service offers look cheap. Ask what happens at the end of the term.
- States and utilities still pay. Some pay upfront per kWh, some pay per year for grid events. These change often. Ask your utility first.
Not tax advice. A tax professional can tell you what applies to you.
Or a generator
| Home battery | Standby generator | |
|---|---|---|
| How long it runs | Hours to a day or two, longer with solar | As long as there's natural gas or propane |
| Switchover | Near instant | Ten to thirty seconds |
| Everyday value | Time shifting, solar, grid programs | None. It waits. |
| Upkeep | Very little | Oil changes, weekly self-test runs |
| Noise and fumes | None | Yes, and it has to sit outside with clearances |
| Big loads | Needs a lot of battery for central air or electric heat | A 22 kW unit runs most houses |
If your outages last days, not hours, and you have gas, a generator still makes a lot of sense. Plenty of people end up with both: a battery for the daily savings and the short outages, a generator for the ice storm.
What to ask the installer
- Is this whole-home or essentials backup, and which circuits are on it?
- Will it start my air conditioner, well pump or sump pump? Do I need a soft starter?
- How much of the battery do I keep for backup when it's also doing time shifting or grid events?
- Can it recharge from solar during an outage, and from a generator?
- What does the warranty cover: years, cycles, throughput, and the capacity left at the end?
- Who services it, and what happens if the installer goes out of business?
- Does my utility or state pay anything, and does that change how the battery runs?