Electric
Checking battery health before you buy
7 min read
On a used electric car a single figure decides a substantial part of the price: the state of health of the battery. It can be established — and a seller who refuses is already telling you something.
What state of health means
State of health, usually abbreviated SoH, states how much of its original capacity the battery still holds. A figure of 90 per cent means the car still stores nine-tenths of the energy it did when new — and travels correspondingly less far.
The decline is not even: it typically falls faster in the first year and more slowly afterwards. A car still clearly above eighty per cent after five years has been treated well.
How to get the figure
There are several routes, and they differ in effort and reliability.
- In the car's own menu: some makers display the figure directly. The most convenient route, but not present on every model.
- Through a franchised workshop: a battery certificate from the diagnostic tool. The most reliable answer and worth the money on an expensive car.
- With a reader on the diagnostic port and a suitable app. Cheap, but accuracy depends on the model.
- As an approximation: compare the indicated range at full charge with the new-car figure. Imprecise, because the display factors in driving style — but usable as a first indication.
The warranty is the second figure
Almost all manufacturers give the traction battery its own, longer warranty than the rest of the car — commonly eight years or a mileage limit, whichever comes first, with a guaranteed remaining capacity. On a used car that warranty is worth real money, and it usually transfers to the next owner.
Ask for the first registration date and work out how long the warranty still runs. A car with four years left on the battery is a different proposition from one with four months, even if the two look identical.
What accelerates ageing
It is worth asking the previous owner, because three habits noticeably accelerate ageing: frequent fast charging, routinely charging to a hundred per cent, and standing for long periods full or empty. A car mostly charged at home to eighty per cent is in better shape than one with the same mileage from the fast charger.
Older models without active battery cooling are more sensitive to both heat and frequent fast charging. On those cars, measuring state of health matters especially.