Home Battery Calculator (2026)

What this estimate leaves out

Each point below pairs a theme that owners of home batteries describe (from a qualitative scan of recent owner posts, which we did not count or verify one by one) with a fact from a primary source.

1. Real efficiency can be lower than the sheet. Sheet figures are for a new battery at about 25 °C and a set power: Enphase prints 90% (AC to battery to AC at 50% power), Tesla 89% for Powerwall 3 (solar to battery to home at 3.3 kW), FranklinWH 90% (at 3 kW). One EPRI field report (December 2024) measured throughput efficiencies of about 66% to 82% in 4 homes with lithium iron phosphate batteries in 2023, and says throughput efficiency is not the same thing as round-trip efficiency.
2. Capacity fades. A 2024 Nature Energy study of 21 German home systems (mixed chemistries, up to 8 years) found they lose about 2 to 3 percentage points of usable capacity per year on average. Warranties promise a floor, not a curve: FranklinWH says at least 70%, Enphase 60%.
3. A warranty can end early. Enphase: up to 15 years or 6,000 cycles, whichever first. FranklinWH: 15 years or 60 MWh, and it drops to 4 years if the system is not registered or stays offline over 90 days. sonnen: 10 years or 10,000 cycles.
4. Power limits are separate from energy. A battery can hold kWh and still be unable to start a big motor. Tesla prints the start capability of Powerwall 3 as 185 LRA, which is amps. Its 15.4 kW off-grid figure is for solar only, between -20 and 25 °C, and needs an 11.5 kW rating and an 80 A breaker.
5. Which circuits are backed up is a design choice. Tesla's sheet shows whole-home backup with some gateways and partial backup with another. Owners often report being surprised that air conditioning or a dryer was left off the backed-up panel. Ask for the list of backed-up circuits in writing.
6. Apps and quotes can show long runtimes. Some assume solar recharge. This page uses your watts and counts no solar unless you type it.
7. Prices are quote-level. EnergySage reported $1,130/kWh for home batteries in H1 2026 and its article does not say what that includes. Lawrence Berkeley National Laboratory's 2026 update finds that paired solar-plus-storage cash systems cost $2.1/W of solar more than stand-alone solar, before incentives, with about 80% of that price data from California. We found no verified national low, median or high price for a battery-only installation: UNVERIFIED.
8. Incentives change. The Section 25D homeowner credit is not allowed for expenditures made after December 31, 2025, and an expenditure counts as made when installation is completed. Utility programmes pay you for letting the utility use the battery, so they are conditions of use, not rebates, and funding can run out: APS $110 per kW for the May to October season (up to 60 events, usually 1 to 4 hours between 4 and 10 pm), TEP $120 per kW per summer or winter season (up to 100 events a year), Mass Save $275 per kW (up to 60 events of at most 3 hours, June to September, 3 to 8 pm), Hawaiian Electric $400 per kW upfront (a daily two-hour window; the page gives both a 5 and a 10 year commitment, so confirm). They are not counted unless you type them.
9. Safety and permits are local. A certified product is not a permit, and placement rules differ by town: ask your building department. In November 2025 CPSC recalled about 10,500 Powerwall 2 units after 22 overheating reports, including 6 of smoke and 5 of fire, with no injuries reported; Powerwall 2 is printed on the label. We found no published fire rate per installed home battery, so we give none, and recall counts cannot be turned into one.
10. Delays and approvals. Owners describe waits for utility approval after the install is done. Not modelled.
11. Standby and software limits. Owners report standby use and power limits set in software. Type your own standby figure; fixed charges and demand charges on your tariff are not counted.

The federal credit and your payback

There is no federal 30% credit for a home battery installation completed after December 31, 2025. The IRS says paying earlier does not help if the installation is completed later. This calculator therefore counts no federal credit. Our incentives by state guide lists state and utility programmes we have verified.

How the calculator works

• Bill savings. Energy delivered per day is the smallest of: usable energy, the amount you choose to move, discharge power times the expensive hours, and charge power times the charging hours times efficiency. Energy taken in is delivered energy divided by round-trip efficiency. Net per day = delivered kWh x the price it avoids - taken-in kWh x the price it pays or gives up - wear - standby. Net per year = net per day x days.
• Backup runtime. Hours = usable energy x (charge - reserve) + any solar kWh you typed, divided by average load plus standby draw. Two checks come first: running watts against continuous kW, and running watts plus the largest starting load against the short-surge kW. If a check fails there are no hours.
• Payback. Net price = quote (or size x price per kWh) - incentive. Each year's saving = the first-year saving x remaining capacity x any price change, plus programme income. Capacity falls in a straight line by the points you enter. Years counted = the warranty, or fewer if a throughput or cycle limit is reached first. Payback is the point where the running total reaches zero.
• Not modelled: replacement, resale, tax, finance cost, backup as a dollar value, demand and fixed charges, changes in your use, and anything after the warranty.

Average home electricity use for comparison is from the EIA 2020 Residential Energy Consumption Survey: 10,566 kWh per household per year for the US, which is 28.87 kWh a day (CALCULATED: annual divided by 366, since 2020 was a leap year). Climate regions in the drop-down use the same table.

Frequently asked questions