- Batteries have two ratings: energy (kWh), how much they store, and power (kW), how much they can run at once.
- Lawrence Berkeley National Laboratory data shows 37% of US residential solar systems installed in 2025 included a battery, up from 25% in 2024.
- The median residential battery in that data stored about 13.5 kWh.
- Batteries pay best with time-of-use rates, low export credit or demand charges; with full retail net metering, they rarely pay on savings alone.
Step 1: Decide what the battery is for
Every sizing decision flows from the job you want the battery to do:
- Backup power: keep selected circuits running during outages.
- Bill savings: store cheap solar or off-peak grid power and use it during expensive peak hours.
- Self-consumption: use more of your own solar where exports are credited at low rates.
- Grid programs: some utilities pay battery owners to discharge during grid stress, sometimes called virtual power plant programs.
Many owners want a mix, but one usually dominates. Backup sizing is driven by your critical loads and outage length. Savings sizing is driven by how much energy you use during peak hours.
Step 2: Size for energy (kWh)
For backup, add up the daily energy your essential loads use. Typical ranges look like this, but check your own appliances' labels or measure them:
| Essential load | Rough daily energy | Notes |
|---|---|---|
| Refrigerator | 1–2 kWh | Older units can use more |
| Lights, internet, phone and laptop charging | 1–2 kWh | LED lighting keeps this low |
| Gas furnace blower | 2–5 kWh | Depends on run time |
| Well pump | 1–3 kWh | High starting surge |
| Medical or home-office equipment | Varies | Check device ratings |
| Central AC or heat pump | 15–40+ kWh | Usually the deciding factor in whole-home backup |
Then account for losses. Usable capacity is normally a little less than nameplate capacity, and round-trip efficiency, the energy you get back out versus what you put in, is typically around 85–90% for lithium-ion home batteries.
Step 3: Size for power (kW)
Energy tells you how long; power tells you how much at once. A battery with plenty of kWh but a low continuous kW rating may not be able to start a well pump or air conditioner. Check two numbers:
- Continuous output (kW): must exceed the combined running load of everything on at the same time.
- Peak or surge output: must handle motor start-up spikes from pumps, compressors and some appliances.
Our home battery sizer walks through both, and LBNL data shows typical residential battery power ratings rising sharply in 2025, reflecting demand for whole-home backup.
What a home battery costs
Battery prices vary widely with capacity, brand, whether it is installed alongside solar, and how much electrical work is needed (a backup gateway, critical-load subpanel or main panel upgrade). LBNL data offers a useful benchmark: in 2025 the median US residential solar-only system cost about $3.60/W, while solar-plus-storage systems cost about $4.90/W. For a median 7.7 kW system, that difference is:
($4.90 − $3.60) × 7,700 W = about $10,000 for a median battery of around 13.5 kWh, or roughly $740 per kWh of storage.
That is a rough derived figure, not a quote; your price may be higher or lower, especially for a retrofit onto existing solar or for multiple batteries. US federal homeowner credits that once covered battery storage ended after 2025, but some states and utilities offer storage rebates or performance payments. See our incentives page.
When a battery pays for itself: a worked example
Suppose a household has solar and is on a rate with an expensive evening peak. Each day it charges 10 kWh from solar that would otherwise be exported and uses that energy during the peak instead of buying from the grid. Round-trip efficiency is 90%, so storing 10 kWh of usable energy takes about 11.1 kWh of solar.
Scenario A: peak rate 40¢, export credit 8¢
- Value of avoided peak purchases: 10 kWh × $0.40 = $4.00 a day
- Lost export credit: 11.1 kWh × $0.08 = $0.89 a day
- Net: $3.11 a day × 365 = about $1,136 a year
- Payback on a $10,000 battery: about 8.8 years
Scenario B: peak rate 30¢, export credit 15¢
- Avoided purchases: 10 × $0.30 = $3.00 a day
- Lost export credit: 11.1 × $0.15 = $1.67 a day
- Net: $1.33 a day × 365 = about $487 a year
- Payback: more than 20 years, beyond most battery warranties
Scenario C: full retail net metering
If exports earn the same as what you pay for imports, storing solar earns almost nothing and loses about 10% to efficiency. The battery's value is backup alone.
Lifespan and warranties
Home batteries are commonly warranted for about 10 years, often with a guarantee that capacity will not fall below a stated percentage, frequently in the 60–70% range, by the end of the warranty. Some warranties also cap total energy throughput. Read both limits: daily cycling for savings uses up throughput faster than occasional backup use. Lithium iron phosphate (LFP) chemistry, now common in home batteries, generally offers good cycle life and thermal stability.
Battery versus generator for backup
| Battery | Standby generator | |
|---|---|---|
| Long outages | Limited by capacity unless solar recharges it | Runs as long as fuel lasts |
| Everyday bill savings | Possible with the right rate plan | None |
| Noise and emissions | Silent, none on site | Noisy, on-site combustion |
| Maintenance | Minimal | Regular servicing and fuel |
Practical checklist before you buy
- Pull 12 months of usage data and identify your peak-hour consumption.
- Confirm your current and likely future rate plan and export rules.
- List the circuits you truly need in an outage.
- Check usable kWh, continuous kW, surge kW, round-trip efficiency and warranty terms.
- Ask whether your existing solar inverter is compatible, or whether you need an AC-coupled battery.
- Compare at least two or three itemized quotes; you can request free installer quotes that include storage options.
Frequently asked questions
How big a battery do I need for my home?
For essential-circuit backup, many homes need 10 to 15 kWh for a day of careful use. Whole-home backup with air conditioning or electric heating can need two or more batteries. For bill savings, size the battery to your typical peak-hour usage.
Can a battery power my home during an outage without solar?
Yes, until it runs out. Without solar to recharge it, the battery's stored energy is all you have, so a long outage may require conserving power or a backup generator.
Does adding a battery make sense under full net metering?
Usually not for savings alone, because exports already earn full retail value. A battery may still be worth it for backup power or if your utility pays for battery participation in grid programs.
How long do home batteries last?
Warranties typically run about 10 years with a minimum capacity guarantee. Many batteries will keep working beyond that at reduced capacity.
Run your own numbers
Plug your bill, prices and climate into our free home battery sizer — every assumption is editable.
This guide is general information, not financial, tax or engineering advice. Prices and incentives change — confirm with qualified local professionals and official program sources. See our methodology and disclosures.