What problems can an electric car battery have?

1. Wear: every battery loses capacity

Every battery wears — that is normal. The part of the original capacity that is left is called the SOH (State of Health). A car that did 400 km when new still does about 340 km at 85% SOH. The wear is caused by:

• Age — even a battery that sits still ages slowly
• Charge cycles — every full charge-discharge cycle counts a little
• Fast charging — regular fast charging stresses the cells more than charging at home
• Heat — heat is a battery's biggest enemy; often sitting fully charged in the sun counts too
• Extremes — often leaving the battery completely full or completely empty

2. Cell imbalance: one weak cell slows everything down

A battery pack consists of dozens to hundreds of individual cells. They should all have exactly the same voltage. If one cell deviates, the weakest cell determines how much the whole battery can charge and deliver — just like the slowest walker in a group.

The difference between the highest and lowest cell voltage (the cell balance, measured in millivolts) is therefore one of the earliest warning signs. A healthy battery is usually below 50 mV; a large difference can point to a cell that is deteriorating — often long before the car itself shows an error.

3. Faulty cells or modules

If a cell really fails, you notice a sudden drop in range, loss of power, error messages or a car that switches to limp mode. Repair usually means replacing a module — technically well possible, but costly. The earlier a weak cell is spotted, the more options you have.

4. Hidden defects when buying

This is where most people lose money. Watch out for these pitfalls:

• The mileage says little — charging behaviour and heat determine the wear, not just the kilometres
• The charge percentage on the dashboard is not health — "100% charged" only means the remaining capacity is full
• "The battery is still fine" — without a measurement that is an opinion, not a fact
• Swapped batteries — sometimes a car contains an older or different battery than it originally had. During our measurement we check whether the chassis number inside the battery system matches that of the car
• Factory warranty has limits — battery warranty usually applies up to a certain age/mileage and only below a certain health threshold; above that, wear is not covered

5. Heat and the cooling system

Modern batteries have their own cooling and heating system. If it does not work properly, the battery wears faster and the car may reduce power. During the measurement we also read the battery temperature and the voltage of each cell — anomalies stand out immediately.

How to keep the battery healthy

What a measurement tells you

Our measurement reads directly from the car's battery system: the health (SOH), the cell balance, the temperature, the capacity and the mileage — and puts it on a certificate with QR authenticity check. Within minutes you know what is really in the car.