Checking battery health on a used electric car
On a used electric car the battery is the part that matters most, both for how the car will serve you and for what it is worth. A battery slowly loses capacity over the years, and that is normal. What you need to learn is how much has been lost and how the car was treated.
What battery health means
The usual measure is state of health: how much energy the battery can store compared with when it was new. A lower figure means a shorter range on a full charge. Other things matter too, such as the ability to deliver power and charge quickly, and how evenly the cells age.
A battery is not a fuel tank that suddenly fails. It typically fades gradually, and many batteries last for years of normal use. Still, how a car was used and charged affects the rate.
What speeds up ageing
- Frequent use of fast charging, especially at high battery levels.
- Regularly charging to full and leaving the car in that state, or leaving it almost empty for a long time.
- Long exposure to heat, such as in hot climates without shade.
- Many years of age, regardless of use.
None of these is a deal-breaker alone. Together with a high mileage, they are a reason to look more closely.
How to find out
- Read the display. Many cars show an estimated range or a battery health indicator. Note the range on a full charge, and keep in mind that this number is an estimate affected by weather and recent driving.
- Ask for a battery report. An authorised workshop or a specialist can read the battery's state of health from the car's systems. Some sellers can supply a recent report. Treat a report that is old or undated with caution.
- Ask about the warranty. Many makers cover the battery for a number of years or kilometres against excessive loss of capacity. Ask for the exact terms and whether they pass to a new owner. See documents when buying.
- Test it. On a test drive, notice how the range estimate falls compared with the distance driven, and test whether the car charges properly if you can. Read the test drive checklist.
- Check the history. Service records, charging habits and any previous battery repairs or replacements are useful. A battery that has been replaced under warranty is not necessarily bad, but the paperwork should be there.
Warning signs
- A seller who cannot or will not say how the car was charged or provide any records.
- A big gap between the range displayed and what the car did when new, with no explanation.
- Warning lights relating to the battery or the high-voltage system; see dashboard warning lights.
- Signs of accident damage under the car, where the battery is placed; see signs of accident repair.
- Charging that is unusually slow or stops early, or a charge port with damaged pins.
Batteries that are leased or separate
With some cars the battery is rented or financed separately from the car. Make sure you understand who owns it, what the monthly cost is and what happens if you sell. This must be clear in the contract before you pay.
Battery and price
A car with a healthy battery and a valid warranty is worth more than one with a degraded battery, even if the age and mileage are the same. Use that in your negotiation, and remember that advertised prices are asking prices, not the amount cars actually sell for. See negotiating the price and how to use market prices. The fair price tool can show how a car compares with similar ones.
Replacing or repairing a battery
A full replacement is a major expense, and some faults can be repaired at module level. Never work on the high-voltage battery yourself. If you want a view of the potential cost, ask an authorised workshop before you buy. The bigger picture is in EV basics for buyers.
What to remember
- Some capacity loss over time is normal; the amount is what matters.
- Ask for a recent battery report and the warranty terms.
- Fast charging, heat and long full or empty periods speed ageing.
- Check the underside for impact damage.
- A weak battery should lower the price you pay.
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