On a used petrol car you check service history and listen to the engine. On a used EV, one component holds most of the value, and it degrades quietly. The good news is that battery condition is measurable if you know what to ask for.
- Ask for a state-of-health report from a dealer diagnostic, and note who produced it.
- Most healthy packs lose a modest percentage in the first years then settle to a slow decline.
- A full-charge range readout is a clue, not a measurement, because it is based on recent driving.
- Check remaining battery warranty. It often transfers and is worth real money.
Ask for a state-of-health reading
State of health, usually written as SoH, expresses current usable capacity against original capacity. Franchised dealers can pull it from the manufacturer diagnostic. Independent specialists can often read it with third-party tools. Ask for a printout or screenshot with the date and mileage on it.
Treat a refusal as information. A seller who will not produce a reading on a car with a healthy pack is unusual.
Understand what normal degradation looks like
Lithium-ion packs typically show a relatively quick early settling period, then a long slow decline. What matters is not a single number but whether the number is consistent with the car’s age, mileage and use. A high-mileage car that lived on slow home charging is often healthier than a low-mileage car that was fast charged daily.
| Signal | What it suggests | How to check |
|---|---|---|
| SoH well below similar cars | Hard life or a weak pack | Manufacturer or third-party diagnostic |
| Rapid taper when fast charging | Cell imbalance or thermal issues | Observe a real DC session |
| Large gap between predicted and actual range | Recent heavy use, or genuine capacity loss | Drive a fixed route and compare kWh used |
Do a real charging test
If you can, watch the car take a DC fast charge from a low state of charge. A healthy pack ramps up smoothly and holds a sensible rate to around 60 or 70 per cent. A pack that never gets near its rated power on a known-good charger, or that tapers almost immediately, deserves a closer look.
The range estimate is a prediction based on recent consumption. A car that has been doing short cold trips will show a pessimistic figure even with a perfectly healthy battery. Use energy consumed over a known distance instead.
Check the warranty position
Battery warranties commonly run for a set number of years or kilometres and promise a minimum state of health. Confirm the start date, whether it transfers to you, and what the threshold is. A car two years from the end of a transferable battery warranty is a different proposition to one just outside it.
Paperwork worth seeing
Service records, any battery-related software updates, and evidence of how it was charged. Some cars log charging history that a dealer can summarise. None of this is conclusive on its own, but a consistent picture is reassuring.
Frequently asked questions
How do I check the battery health of a used EV?
Ask for a state-of-health reading taken from a manufacturer or third-party diagnostic, dated and with the mileage recorded. Back it up by watching a real DC fast charging session and by measuring energy used over a fixed route.
What is a normal state of health for a used EV?
Packs typically show a relatively quick early settling period, then a long slow decline. Judge the figure against comparable cars of the same age, mileage and charging history rather than against a single universal threshold.
Does the battery warranty transfer to me?
On most manufacturers it does, but confirm it in writing. Check the start date, the remaining term, and the state-of-health percentage the warranty guarantees, because that floor is what actually protects you.
