That's why we test electric car batteries before sale

Buying a used electric car or plug-in hybrid should be as safe as buying a petrol or diesel car. By showing the health of the battery in our ads, we make it easier for the buyer to make informed decisions.

The test is based on information that is already in the car. The most important number is the State of Health (SoH), a measure of the battery's condition compared to when it was new. SoH does not tell you how quickly the battery is wearing out, but how it is performing right now.

“SoH provides the best available picture of the battery’s condition. It shows how much capacity is left and gives a good indication of how the battery will be experienced in everyday life,” says Martin Reinholdsson, technical expert at Kvdbil .

The information is taken from the car's battery management system, which continuously monitors factors such as voltage, current and temperature. The system uses data from the battery's many individual cells to calculate the battery's health, with the condition of each cell affecting the whole. In practice, a battery pack only works as well as the interaction between the cells allows. The same system is used by the car to optimize charging and discharging, balance the cells and protect the battery from overheating.

Clear star rating

To make the information easy to understand, the result is presented as a star rating between zero and three stars.

⭐⭐⭐ Very high capacity, fast charging, long life.

⭐⭐ Good capacity with many years left, but slightly more sensitive to cold.

⭐ Limited capacity, best suited for shorter trips.

⛔ Requires further verification or more information.

The battery certificate also shows the exact SoH percentage.

Read more: How we test the battery

Several things affect battery life.

All batteries age over time, but how quickly this happens depends on several factors. Studies show that batteries typically lose about 2 percent of their capacity per year with normal use.

At the same time, wear is affected by temperature, how the battery is charged and how the car is used. Frequent fast charging, for example, can increase wear, while extreme cold or heat can also affect the battery's lifespan.

– Just like with much other technology, batteries are best when you avoid extremes. Not always fast charging and charging to around 80 percent in everyday life can help keep the battery in good condition over time, says Martin Reinholdsson.

Another characteristic of batteries is that wear and tear is often slow at the beginning of the life cycle, but increases as the battery gets older. This means that range usually decreases gradually over many years, but somewhat more quickly towards the end of the battery's life.

Great importance for second-hand value

For rechargeable cars, the high-voltage battery is one of the most valuable components. Therefore, its condition is of great importance for both the driving experience and the car's resale value. Battery tests show that quality varies between different manufacturers.

“The battery is a central part of the experience of a rechargeable car. By making its condition more transparent, we want to contribute to a safer and more informed car purchase,” says Martin Reinholdsson.