EV battery health (SoH): how to interpret the numbers on a used EV

Short answer: SoH (State of Health) states how much of the battery's original capacity remains, as a percentage. It is the single most important number when assessing a used EV, because it governs both range and resale value. Always ask for a fresh SoH measurement done with diagnostic equipment — do not settle for the range shown in the display.

What SoH actually means

All traction batteries gradually lose capacity with age and use — that is normal and expected. SoH compares today's measured capacity with the capacity the battery had when new. Degradation is typically fastest in the battery's first years and then flattens out, so a few percent lost early does not mean it continues at the same pace.

What affects battery health?

• Age and mileage — the fundamental driver
• Charging habits — frequent fast charging and long storage at full or empty charge wear more than steady home charging
• Climate — strong heat is worse for the battery than cold; cold reduces range temporarily but does not damage it
• Usage pattern — many deep discharges wear more than steady everyday driving

How SoH is measured

A real SoH measurement is done with diagnostic equipment that reads the battery management system's data — cell condition, voltage balance between modules and measured capacity. That is a completely different level of precision than the display's range estimate, which mostly mirrors the previous owner's driving style. A good report also shows whether the cells are in balance, or whether individual modules stand out negatively.

What we see most often at the workshop

The most common misunderstanding we meet is that "long range in the display" is read as a good battery. We have measured cars with a fine display figure and mediocre SoH — and the reverse. The second most common is worry about normal degradation: a battery that has lost a few percent over a few years is behaving exactly as expected. What we actually look for is imbalance between modules and an abnormal drop for the age — that is what separates a good buy from a bad one.

Before you buy a used EV

Ask for a fresh SoH report, check that the battery warranty follows the car, and preferably combine it with a full pre-purchase inspection. We carry out battery health measurement and EV servicing on all brands.

Considering a used EV? Call 41 17 32 24 and book a battery check before you sign.