Used EV battery health: how to check it before you buy

What state of health means

State of health, SoH, is how much of the original usable capacity remains. Two identical cars with the same mileage can be far apart, and nothing about it shows from the outside. The range estimate is not that figure, and an app screenshot is only a hint.

Every lithium-ion pack loses some capacity with time and use, and that is chemistry, not a defect. Two clocks run at once: calendar ageing, driven by time, heat and how full the pack is kept, and cycle ageing, driven by use. Capacity usually falls fastest early, as the chemistry settles, then flattens into a long, slow decline.

The figure is also harder to get than it sounds. Some cars show an estimate on a screen or in an app, inferred by the battery management system, and it moves with temperature, recent charging and software updates. Some expose it only through a dealer or specialist diagnostic that reads cell-group data, and some expose nothing useful to the owner.

What a proper check covers

• A state-of-health figure in writing, from a dealer or specialist test, rather than the seller's number or an app screenshot
• The conditions of that test: a warm pack at a known state of charge, because a cold pack gives up less of its energy and the estimate moves with temperature and recent charging
• A comparison with other cars of the same model and age, rather than the number on its own
• Stored codes, above all P0A80, which means the pack has degraded past the manufacturer's threshold
• What remains of the battery warranty: the age limit, the mileage limit and the capacity threshold at which it pays out
• How the car has been charged: a pack rapid-charged almost exclusively, in a hot climate and to a high state of charge each time, has had a harder life than one charged mostly at home
• A documented service history, which the battery warranty depends on

Step by step

1. Ask the seller for a written state-of-health report from a dealer or an independent specialist. Do not take the seller's number on trust, and do not settle for being told the battery is like new.
2. Find out what your model can show: an estimate in a menu or an app, only a service diagnostic, or nothing useful at all. If you arrange the test yourself, have it done on a warm pack at a known state of charge, so a cold morning does not skew the reading.
3. Have the car scanned for stored codes. P0A80 did not appear overnight, and clearing it repairs nothing. A reader that reports no codes may simply not query the modules where EV faults live.
4. Get the warranty booklet for that car in your country. Check the capacity threshold, the age and mileage left, and what is excluded, such as flood damage, unapproved charging equipment or ignored warnings. The battery warranty usually follows the vehicle rather than the owner.
5. Ask for the service history. The warranty holds as long as the schedule was followed and documented, and on an EV that record is what a buyer uses to judge the battery.
6. Ask how the car has been charged, whether all software updates have been run, and what it does in winter and whether it has a heat pump. Look up whether the model has open recalls.

A real answer, or only a hint?

• A written state-of-health report from a dealer or specialist, done on a warm pack at a known charge: the one document that answers the question.
• An app screenshot or a figure in a menu: a hint, an estimate that moves with temperature, recent charging and software updates.
• The range estimate on the dashboard: not state of health. It blends capacity with recent consumption, temperature and driving.
• Lower range on a cold test drive: not degradation. Cabin heating and a cold pack explain most of it, and it comes back.
• A generic reader shows no codes: not a clean bill. Many EV faults live in modules a basic reader never queries.
• P0A80 stored, or an amber traction battery fault lamp: P0A80 is capacity past the manufacturer's threshold, and the lamp is a fault in the cells or their management, not a worn pack. Either one needs a specialist reading before you buy.

What people get wrong

Reading the range display as battery health. The range estimate blends the pack's capacity with recent consumption, the temperature and the way the car has been driven, so a summer test drive flatters it and a winter one does the opposite. A winter range drop is not degradation. State of health is the figure that matters, and it has to be measured, not guessed from the range.

When to get a specialist test

Get a specialist state-of-health test before you buy if the seller has no written report, if the figure is clearly lower than other cars of the same model and age, or if P0A80 is stored. Choose a dealer or EV specialist that can read cell-group data. A car with signs of flooding, or a pack casing that has been struck, needs specialist assessment before it is driven, charged or stored inside. Treat damaged orange cabling as live and keep away from it: high-voltage work is for trained technicians only.

Read next

• P0A80: traction battery degraded past the manufacturer's threshold
• EV range in cold weather: why it drops, and what helps
• Used car paperwork: history report, title and service records

This page is general information and does not replace a professional assessment. Symbols, codes and behaviour vary between makes. Always check the handbook for your own car.