How long do home batteries last?

EnergySage says most solar batteries keep performing well for 10 to 15 years before they need replacing, and that a battery doesn't stop working when its warranty ends; it just holds less energy.

Real-world data backs up a gradual fade. A 2024 study in Nature Energy tracked 21 home battery systems in Germany for up to eight years and found they lost about two to three percentage points of usable capacity a year on average. Most were first-generation products, aging varied a lot from one battery to the next, and a few reached 80% of their original capacity after five to seven years.

Keep the battery online. Tesla says Powerwall's warranty may be limited to four years if its internet connection is down for an extended period and Tesla can't reach the owner, and Generac requires an internet connection for the whole warranty. At Tesla's 70% floor, a 13.5 kWh Powerwall is guaranteed to hold at least 9.45 kWh at year 10. Compare models in Powerwall 3 vs. Enphase vs. FranklinWH.

They can limit it. Tesla rates Powerwall 3 to operate from -4°F to 122°F and says it may limit charging or discharging at the extremes to protect battery life. Enphase rates the IQ Battery 5P to charge from -4°F to 122°F, with an optimum range of 32°F to 86°F, and FranklinWH lists -4°F to 122°F for its aPower.

Northern Illinois occasionally drops below that: O'Hare hit -23°F during the January 2019 polar vortex. An attached garage or basement keeps a battery in a milder range than an exterior wall, so ask your installer where yours will perform best. Placement also has fire code limits; see are home batteries safe?

To get the roughly $300 per kWh storage rebate, Illinois batteries now join a utility virtual power plant. ComEd's program asks for five consecutive summer seasons, June 1 through September 30, and Ameren's dispatches batteries on summer weekdays. See ComEd and Ameren virtual power plants.

Those discharges add cycles, and warranties count use differently. Tesla's unlimited-cycle coverage applies to solar self-consumption, time-based control and backup, with a 37.8 MWh cap for other uses; Enphase counts cycles, and FranklinWH counts megawatt-hours. We found no manufacturer statement on how ComEd or Ameren dispatches count, so ask your installer to show you, in writing, how the program affects your warranty.

Usually nothing dramatic. The battery keeps working with less capacity, so it covers fewer hours of backup or evening use. When it no longer meets your needs, you can replace the battery, often reusing the rest of the system. Tesla says it tries to extend a battery pack's useful life before sending it for recycling.

Prices change over a decade, so don't budget a replacement from today's numbers. For current prices, see what a home battery costs.

• Mind the temperature. Batteries age best in a moderate range, which is why indoor or garage spots help in Illinois.
• Avoid keeping it full or empty all the time. In Sandia National Laboratories testing, lithium iron phosphate cells degraded less when held at a lower state of charge and cycled across a narrower range.
• Keep it connected so warranty monitoring and updates work.
• Pick a backup reserve that fits your outage risk instead of cycling the battery to zero every day.