Do electric cars need servicing?
No oil changes, but electric cars still need brake, coolant, filter, tyre and 12V battery attention. Here is what a proper EV service covers.
Read article →The short answer
State of health (SOH) is the percentage of its original capacity an EV battery can still hold. A battery at 85% SOH holds 85% of what it held when new, so range is correspondingly lower. It is measured with a dedicated battery test, such as the AVILOO test we use, not read from the dashboard, and it is the key number to know when buying a used EV.
Every rechargeable battery loses capacity as it ages, and an electric car's battery is no exception. How much it has lost is the single biggest factor in a used EV's value and usefulness. That loss is expressed as state of health, or SOH.
What state of health means
SOH compares the battery's current usable capacity with its capacity when new. If a pack held 40 kWh new and can now hold 34 kWh, its SOH is 85%. The car's range falls in roughly the same proportion, all else being equal. SOH is separate from the "state of charge" you see on the dashboard, which is simply how full the battery is right now.
What affects battery health
- Age. Batteries degrade with time even when the car is barely used.
- Distance and charge cycles. More use generally means more wear.
- Heat. High temperatures, especially when combined with a full charge, are hard on cells.
- Fast charging. Frequent DC fast charging can age a battery faster than slower charging, depending on the car.
- Charging habits. Regularly sitting at a very high or very low charge can add stress.
- Battery design. Chemistry and thermal management differ widely between models, so there is no single rate of decline for every EV.
How battery health is measured
Dashboard range figures and bar gauges are rough, and can be affected by temperature, driving style and software. A proper reading uses a dedicated battery test connected to the car, which reports the pack's capacity. We use the AVILOO battery test, which tests and reports on the battery of all makes and models of EV, and we explain the result. See EV and hybrid servicing.
Warranty
Many EVs carry a separate battery warranty, often for a number of years or a set distance, and typically covering capacity falling below a stated level. The terms vary between makes and may not carry over to used imports, so check the actual terms for your car and ask the seller for evidence. Do not assume a warranty exists.
Before you buy a used EV
- Ask for the battery's SOH and how it was measured, not just the dashboard range.
- Get an independent test, such as the AVILOO battery test, as part of a pre-purchase inspection with a thorough road test and a detailed report. See pre-purchase inspections.
- Check the charging port, cable and charge history where you can.
- Test the 12V battery too. It is a small cost, but a failing one causes big headaches.
- Work out what the range means for you. A lower SOH can still suit a short daily commute.
Looking after the battery you have
- Avoid leaving the car for long periods fully charged or nearly flat, where the manufacturer advises against it.
- Park in shade and avoid heat soak where you can.
- Use fast charging when you need it, but rely on slower charging for routine top-ups.
- Keep software up to date and service the cooling system to schedule.
Frequently asked questions
What is a good state of health for a used EV?
It depends on the car's age, distance and design, so there is no single threshold. What matters is that the reading is measured properly, that it makes sense for the car's age and use, and that the remaining range suits you.
Is the range shown on the dashboard the same as battery health?
No. Dashboard range is an estimate affected by temperature, driving style and the car's software. State of health is measured with a dedicated battery test and reflects the battery's real capacity.
Can you replace or repair a degraded EV battery?
Yes. We do EV battery replacements, upgrades and individual cell replacement, depending on the vehicle. Contact us with the make, model and year and we will tell you what is realistic.
Does fast charging damage the battery?
Frequent fast charging can age a battery faster than slower charging, depending on the car and its cooling. Occasional fast charging when you need it is not a concern for most owners.
Written by the GVI Service Centre team. We are an independent workshop in Penrose, Auckland, servicing petrol, diesel, hybrid and electric vehicles. Facts about NZ rules are checked against NZTA and other official sources at the date shown; always confirm anything important with the source.
