A home lithium battery often lasts 10 to 15 years. Yet many owners don’t know when it is really worn out.
When should you replace yours, and what will it cost? This article covers how long it runs your home, what affects its life, the signs it needs replacing, and the US replacement cost.
How long do solar batteries last for a modern lithium home battery
A lithium-ion home battery often lasts 10 to 15 years. Use that range to plan ahead, not as a promise: two identical batteries can age at different speeds.
LFP batteries, which use lithium iron phosphate, also last 10 to 15 years with daily use. If you are weighing backup power, see battery backup versus generator before you buy.
Old battery, still working
A battery that is getting older is not automatically due for replacement. If it still powers your essential loads for the hours you need, it can stay in service.
Before you decide, check the capacity shown by your system and how long it runs your usual appliances.
The 70% capacity benchmark and why warranty end dates differ
Compare each warranty’s end date, usage limit and capacity promise, not only its 70% figure.
Criterion
Enphase IQ Battery 5P
FranklinWH aPower 2
FranklinWH aPower X
Warranty ends
15 years or 6,000 cycles
15 years or 60 MWh
12 years or 43 MWh
Capacity promise
70% at 10 years, 60% at 15 years
70% for the full term
70% for the full term
Offline batteries can lose warranty cover
Keep the battery connected to the internet. A FranklinWH system offline for over 90 days can drop to a 4-year warranty if the connection isn’t restored after notice. A long Tesla Powerwall 3 outage can cut it the same way if Tesla cannot reach you.
LFP (lithium iron phosphate) batteries often last 10 to 15 years with daily use.
NMC (nickel manganese cobalt) batteries store more energy in the same space.
Lead-acid batteries often last only 3 to 5 years with daily use.
These are estimates, so check the warranty of your model for the real coverage.
Cycling, depth of discharge and temperature
Daily charging and discharging wear a battery cycle by cycle, so heavy daily use ages it faster. Check the cycle count or maximum energy throughput in your warranty.
Deep discharges, emptying the battery nearly flat, also shorten its life, so size it to your appliances. Above 104°F, a Tesla Powerwall 3 cuts its power, and heat shortens lithium-ion life.
How the battery management system protects the battery
Enphase IQ Battery 5P temperature limits
Charging: -4 to 122 °F
Discharging: -4 to 131 °F
Best range: 32 to 86 °F
Battery management system (BMS)
Monitors and controls charge and discharge
Limits stress from cycling, deep discharge and heat
Two identical installs can age differently, depending on how the BMS runs them
What to do
Follow the product guidelines to preserve operation
How many hours a battery runs a house on one charge
Fridge, lights, Wi-Fi and phone chargers: about 34 hours.
Average US home use: about 11 hours.
Central air conditioning (a 5-ton unit, 3.5 kW or more): about 4 hours of continuous running.
Check both numbers
Capacity (kWh)
The energy the battery stores.
It decides how many hours the battery can run your home.
Power (kW)
The energy delivered at any one moment.
It decides which appliances can start and run together.
Example: a fridge (200 W), a gas boiler fan (600 W) and LED bulbs (120 W) draw 920 W together, well under the Tesla Powerwall 3’s continuous 11.5 kW.
Why more solar panels do not extend backup time, but capacity does
Solar panels refill the battery during sunny hours, but they add no energy to what it stores. Capacity sets the backup time.
A 13.5 kWh battery covers a 150 W fridge, 50 W of LED lights and a 10 W router, about 5 kWh a day, for two to three days. So to run longer, choose a battery with more kWh.
Match the battery to your loads
For a few circuits, one battery of 10 to 13.5 kWh is often enough. Connect it to an essential loads panel, a small breaker box that feeds only the circuits you choose.
Whole house or several days: plan for several batteries.
Signs a battery needs replacing, and what to check first
Check these points before you decide to replace the battery:
Shorter runtime is a reason to check, not proof that replacement is needed.
Check the displayed capacity and the state of the system.
Compare the remaining capacity with your warranty threshold. For the Enphase IQ Battery 5P, that threshold is 70% at 10 years and 60% at 15 years, under the stated conditions.
Check these first
Note how often the alert returns.
Contact your installer or support service before deciding.
Compare the displayed capacity with your warranty threshold.
Test how long the battery runs your essential loads.
Replace only if it no longer meets your home’s needs.
What a battery replacement costs in the US before incentives
A 13.5 kWh home battery installed costs about $15,647 before incentives. The price changes with where you live, the equipment you choose, and the work your house needs, such as electrical upgrades.
Ask each installer to show the battery, the installation, and the electrical work on separate lines.
Divide each battery price by its usable kWh, then compare the result with the range of $1,100 to $2,100 per kWh.
Check whether the 30% federal credit appears in the quote, and confirm the battery was placed in service before January 1, 2026.
Ask your tax adviser to confirm your eligibility for the year you install.
Battery age alone doesn’t tell you when to replace it. If the battery still runs your essential appliances for the hours you need, it can stay in service.
Your next step: compare the capacity shown by your system with your warranty threshold, then call your installer before you decide.
Frequently asked questions
Do solar batteries stop charging once the panels produce more than the home uses?
No. Once the battery is full, it stops taking charge, and the extra solar power cannot push it past its capacity.
Panels still refill the battery during sunny hours, and in a system designed for backup, they can recharge it during a power cut too.
Does a battery lose capacity when it sits unused for long periods?
Yes. A battery that sits unused still loses capacity over time, so long idle periods also age it. How fast depends on its chemistry, its temperature and the terms of its warranty, so check those for your model.
Can a second battery be added to an existing system later?
Yes, some systems can take a second battery later, if the inverter and the installed battery are compatible. Ask your installer to confirm that match.
Then size the new battery to the appliances it must run, because those appliances set how much capacity you need.
Does a battery’s warranty transfer to a new homeowner when the house is sold?
It depends on the battery model and its warranty terms, so check the transfer rules before you sell the house. Read them in your warranty, or ask your installer to confirm whether coverage passes to the new owner.