How to check the battery health of a used electric car

Car Tips/Hacks10/28/2026

How to Check a Used EV's Battery Health | Rooster

The battery is the most expensive part of an electric car, so it is the one thing you should never take on trust. The good news is that checking it is quick and cheap. An independent battery health test takes a few minutes, costs from around £40, and tells you the battery’s state of health: how much energy it can hold compared with when it was new.

This guide explains what state of health means, the ways to check it, what a good result looks like for the car’s age, and the warning signs to walk away from.

Last updated 27 October 2026. Figures come from Generational, Geotab, Aviloo and Kwik Fit (see the sources at the end).

Key takeaways

State of health (SoH) is the battery’s usable capacity as a percentage of what it held when new.
The range on the dashboard is an estimate based on recent driving, not a battery health reading.
Independent tests such as the Aviloo Flash Test take a few minutes; Kwik Fit charges £39.99.
Generational’s UK data found a median SoH of 93.5% for four to five-year-old EVs and 85% for eight to nine-year-old cars.
As a rule of thumb, above 85% is healthy for a three to five-year-old EV; below 80% should be reflected in the price.
A seller who will not allow a battery test is a red flag.

What is battery state of health?

State of health (SoH) compares how much energy the battery can store today with how much it could store when new. A 64kWh battery with an SoH of 90% can now hold around 57.6kWh, so you get roughly 90% of the original range.

All lithium-ion batteries lose some capacity over time. Fleet telematics firm Geotab found an average loss of 2.3% a year across more than 22,700 EVs, with many cars losing a little more in the first year or two before levelling off. Our guide to EV battery degradation covers what speeds it up.

Why the dashboard range is not enough

The range figure on the dashboard is a prediction. It is based on the charge level and on how the car has been driven recently, so a car that has been driven gently in summer will show a higher number than one used for motorway runs in winter. A seller can also charge the car to 100% just before you arrive.

The car’s own battery management system does estimate capacity internally, but most cars don’t show it to the driver, and those estimates are not independently verified. Battery tester Aviloo says its tests have found cell damage on cars whose own system reported a healthy-looking SoH.

How to check a used EV’s battery

1. Ask for an independent battery certificate. More dealers now test used EVs before sale. Auction firm BCA checks battery health before cars go to trade auction, and companies such as Aviloo and Generational provide certificates that dealers can pass on. Ask to see the report and check the date: a recent test is worth more than one from two years ago.

2. Book a test yourself. If the seller has no report, you can arrange one. Kwik Fit offers an EV battery state of health check using the Aviloo Flash Test for £39.99, with a digital report. Aviloo says the Flash Test takes about three minutes and covers around 96% of EVs on the road. For a private sale, ask the seller to meet you at a test centre, or make the sale conditional on the result.

3. Ask a main dealer. Some manufacturers include a battery health report in their EV servicing. Kia’s e-Care service plan, for example, includes battery state of health reports. A franchised dealer can usually run a diagnostic check for a fee.

4. Use a diagnostic app for specific models. For the Nissan Leaf, the LEAF Spy app with a compatible OBD reader is the standard way owners read battery health. The Leaf also shows capacity bars beside the charge gauge: a full set is 12, and each missing bar means lost capacity. Apps like this are useful, but they depend on the car’s own data.

5. Do a real-world range test. On a longer test drive, note the charge percentage and miles driven. If a car with a claimed 250-mile range is using 10% of its charge every 12 miles in mild weather, something is wrong.

What does a good result look like?

Battery health depends on age, mileage, climate and how the car was charged, so compare the result with similar cars rather than with 100%.

Car age	Typical state of health	What to do
1 to 3 years	Mid to high 90s	Below 90% deserves questions
4 to 5 years	Around 93% (Generational median)	Above 85% is healthy
8 to 9 years	Around 85% (Generational median)	Price should reflect any shortfall

Generational’s 2025 index of more than 8,000 UK used EV tests found an average SoH of 95.15%, with the spread widening as cars age. Aviloo’s analysis of more than 500,000 tests found that cars that look identical on paper can differ by up to 13.5% in battery health, which is why a test on the specific car matters.

Most manufacturer battery warranties promise to repair or replace the battery if it falls below about 70% within eight years or 100,000 miles. A battery at 80% is not faulty, but it is closer to that line. See EV battery warranties on used cars.

Red flags to look out for

The seller refuses a battery test or keeps postponing it
A low SoH for the car’s age, with no explanation
Rapid charging that is much slower than the model should manage
Warning lights relating to the high-voltage system
Big differences between cell voltages on a diagnostic report
Damage to the underside of the car where the battery sits
A write-off record, which a car check will show

Using the result to negotiate

A battery report is a negotiating tool. If two similar cars are priced the same and one has a noticeably lower SoH, it should be cheaper, because it has less range now and less margin before the warranty threshold. Industry research suggests buyers will pay more for an EV with a certified battery report, which also works in your favour when you come to sell.

Some certificates now come with cover. Since July 2026, Aviloo’s UK certificate includes a battery warranty for qualifying cars: if a second test within 12 months or 20,000km shows the battery has fallen below a calculated threshold, the owner receives £2,700. Check what the dealer’s certificate includes.

For everything else to check, use our used electric car inspection checklist.

Frequently asked questions

How much does a used EV battery test cost?

Kwik Fit charges £39.99 for an Aviloo Flash Test with a digital report. Many dealers include a certificate at no extra cost.

What is a good battery health percentage for a used EV?

For a three to five-year-old EV, above 85% is generally healthy. Generational’s UK data puts the median at around 93.5% for four to five-year-old cars.

Can I check battery health myself?

For some models, yes. Nissan Leaf owners use the LEAF Spy app with an OBD reader, and the Leaf shows capacity bars. For most cars an independent test is the most reliable option.

Is the range shown on the dashboard a good guide to battery health?

No. It is an estimate based on charge level and recent driving, and it changes with temperature and driving style.

Should I buy a used EV without a battery report?

It is a risk. A test is cheap compared with the cost of a battery problem, so ask for one or make the sale conditional on a result.

Sources and further reading

About this guide: Rooster is a UK car insurance provider. This guide is general information for UK drivers. Test prices and warranty terms are set by the providers named and can change, so check them before you book.

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