How long do home batteries last?

A common query when deciding whether to invest in a home battery is: “How long will it last?”

This is a reasonable question. The quick answer most will give is the warranty number, which is 10 years – but there are a few other things to keep in mind when thinking about how long your home battery might last.

• Warranty - Popular battery systems like Tesla’s Powerwall 2 come with a warranty protecting against defects for ten years from the installation date.
• Energy retention - Home batteries lose efficiency as they charge and discharge, just as a mobile phone or laptop battery deteriorates through its lifetime. Tesla’s warranty assures that the Powerwall 2 will retain 70% of its 13.2kWh original capacity 10 years from the installation date when used for household solar backup. A 37 MWh limit in throughput applies if the battery is used for other purposes - eg: participating in a virtual power plant.
• Operation - Lithium-ion home batteries are relatively new, so we will have to wait to see how long they can last in real-world applications. Under the right conditions, experts predict that home batteries could last well beyond the usual 10-year warranty period.

What happens if something goes wrong?

Sticking with the Powerwall 2 example, Tesla offers a number of remedies in the event of a major problem.

• Repair - Tesla’s warranty states that they may use refurbished parts to repair your battery system, or replace the entire battery with a refurbished system. Any repairs carried out will retain the remainder of the original warranty.
• Replacement - A serious fault may require the entire unit to be replaced with a comparable product.
• Refund - You may be offered a refund if the battery cannot be repaired or replaced.

Real-world performance

The best evidence available comes from a trial underway at the Lithium Ion Battery Test Centre at the Canberra Institute of Technology, as part of a project led by ITP Renewables.

They're testing batteries to the limit, cycling a range of systems three times per day to replicate nine years of typical use in their three-year trial. The trial is being conducted in a climate-controlled room which replicates ambient temperatures experienced in the real world.

Results for Tesla’s Powerwall 2 are encouraging, with the system retaining 88% of its initial capacity after 1250 cycles.

In short

A modern lithium-ion battery like Tesla’s Powerwall 2 comes with a 10-year warranty against faults or defects. While the cycle life will deteriorate over time, you can have peace of mind that the battery will retain at least 70% of its starting capacity after 10 years.