How Long Do Solar Batteries Last?

The Energy Saving Trust puts the typical lifespan of a home battery at about 10 to 12 years. Many home battery warranties run for around ten years; some are longer.

But a battery does not simply stop at the end of its life. It gradually holds less. So the more useful question is not only how long it lasts, but how much it will still hold at the end, and what you can do to look after it in the meantime.

Key points

• Typical lifespan is about 10 to 12 years, according to the Energy Saving Trust.

• Batteries fade gradually rather than failing suddenly.

• Warranties usually set a term, a limit on total energy throughput, and a minimum capacity the battery must keep during that time.

• Heat, charging in freezing temperatures and poor siting all shorten battery life.

• A battery that is well sited, well set up and monitored gives itself the best chance.

How battery warranties actually work

A battery warranty is not just a number of years. It usually sets three things:

1. A term in years, commonly ten. Some warranties also set an outer limit measured from the date of manufacture.

2. A maximum total energy throughput, in megawatt-hours. This is the total amount of electricity the battery is warranted to put through. A battery cycled hard every day reaches it sooner. Cover ends at whichever comes first, the term or the throughput limit.

3. A minimum retained capacity that the battery is guaranteed to keep during that period. For example, FoxESS warrants its EP6 and EP12 batteries to keep at least 70 per cent of their nominal capacity for ten years, subject to the throughput limit.

That third point means a battery that is working exactly as warranted may hold only around 70 per cent of its original capacity by the end of the term. That is normal ageing, not a fault.

What affects how long a battery lasts

Heat

High temperatures are hard on lithium batteries. A battery in a hot, unventilated space ages faster. Manufacturers set maximum operating temperatures and, in some cases, make warranty cover conditional on adequate ventilation and clearance. FoxESS, for example, requires at least 300 mm of clearance around its batteries and adequate ventilation.

Cold

Most lithium batteries will not charge below freezing, though they will usually keep discharging. They protect themselves by stopping charging, which is why a battery in a cold garage can look stuck on a winter morning. Some models offer heating options for cold locations.

How hard it works

Every charge and discharge adds to the battery's total throughput. A battery charged overnight on a cheap tariff and discharged every evening does more work than one that only stores summer solar. That is often exactly what you want it to do, but it does use up the throughput allowance faster.

Staying connected

Some manufacturers make warranty terms depend on the battery staying connected to their monitoring, so firmware can be updated. A battery that quietly drops off the internet can lose some of its cover without anyone noticing. Another good reason to keep an eye on your monitoring app.

Signs a battery is ageing

• It runs out earlier in the evening than it used to, on similar days.

• Your monitoring shows it reaching full charge but supplying less than before.

• It reports a reduced capacity, or a state-of-health figure, in the app.

A gradual decline is expected. A sudden drop, error codes, or a battery that stops charging is worth checking. Our guide to why a battery is not charging covers the common causes.

Planning for the battery you will have later

Because batteries fade, it is sensible to size a battery with some headroom, so it still covers most of your evening use in year eight or ten, not just in year one. Our guide to what size battery you need explains how.

What happens at the end

When a battery reaches the end of its useful life, it can be replaced while keeping the rest of the system. With modular batteries, individual modules may be replaceable. Your installer can advise on the options when the time comes.

Batteries must not go in household waste. Your installer or manufacturer should be able to arrange correct disposal or recycling.

How to look after your battery

• Siting: a cool, dry, ventilated spot with the clearance the manufacturer requires. Not a loft, bedroom or escape route.

• Monitoring: keep it connected and check the app occasionally.

• Settings: leave charge limits and reserve settings as they were commissioned, unless you know why you are changing them.

• Servicing: have the system checked periodically, as the manufacturer recommends.

Frequently asked questions

Will my battery last as long as my solar panels?

Usually not. Panels can last 25 years or more; batteries typically 10 to 12. Expect to replace a battery during the life of the panels.

Does a battery stop working when the warranty ends?

No. It keeps working, holding a gradually smaller share of its original capacity.

Is 70 per cent after ten years a fault?

Not if it is within the warranty terms. It is the expected ageing the warranty allows for.

Does charging overnight wear it out faster?

It uses more of the throughput allowance, but that is often what makes a battery worthwhile. It is a trade-off to understand, not avoid.

Request a battery storage assessment. We will size and site a battery so it keeps doing its job for years, not just at the start.