Used Electric Cars – What about Battery Health?

Author: Joachim Geiger

Apr 03, 2024 E-Mobility / Safety on the road / Automotive

Are used electric cars really a risk for users? Reservations are certainly high. More disclosure on drive battery condition could help build the necessary trust. DEKRA expert Michael Tziatzios explains how a special rapid battery test can help buyers and dealers.

The European market for used electric vehicles is in the midst of a crisis. On the one hand, the supply of pre-owned models is very limited. On the other hand, the available vehicles often turn into shelf warmers at dealerships. In Germany, for example – the largest automotive market in the EU – the Federal Motor Transport Authority (KBA) has only recorded around 97,000 ownership transfers of battery electric vehicles (BEV) for 2023 – a share of 1.6 percent of all transfers of passenger cars. However, various online platforms for used electric vehicles also indicate a clear lack of interest in most European markets. This slump has a tangible impact on the growth of the e-fleet in Europe. Current figures from the European Automobile Manufacturers’ Association (ACEA) suggest that, at 1.2 percent, the share of BEVs in the European passenger car fleet (252 million) is not quite making headway. If the European Commission’s Verkehrswende, or mobility transition, is to succeed by 2030, every electric vehicle counts – including pre-owned ones. So far the typical arguments made against used electric cars echo those that have always hampered decision-making for new car buyers: Prices are significantly high, combined with limited ranges, long charging times, and inadequate infrastructure.

The battery is the most important indicator of an electric car’s value

“In fact, we don’t have any relevant buyer demand for high-voltage vehicles,” is the assessment of Michael Tziatzios, Head of Used Vehicle Management at DEKRA Automotive. His analysis focuses, among other things, on the technological aspects of electromobility. “Buyers want their new used car to retain its value. But when battery technology that represents the state of the art today could be outdated tomorrow, doubts arise. The expected lifespan, the procurement of spare parts for the drive units, and the unpredictability of possible defects also seem to deter buyers.” Indeed, the battery is the most important indicator of an electric car’s value. It is therefore logical that customers want to have all the information on the battery’s condition and, consequently, the used vehicle’s range. A helpful indicator is the so-called State of Health (SoH). This metric indicates how much of the battery capacity of the new vehicle is still left after a certain period of use. A SoH of 80 percent would imply that a battery with an original capacity of 80 kWh now only has 64 kWh left when fully charged.

Good consulting can counteract customers’ doubts

“Customers want to be able to rely on the quality of the drive battery in a used vehicle. Dealers have to adapt,” says Michael Tziatzios. A good consultation to counteract the customer’s reservations is also in the dealer’s interest. The purchasing rights in the EU member states trace back to the directive for the sale of goods adopted by the European Parliament in 2019. Essentially, when buying a used e-car, a dealer is also obligated to provide consumers with comprehensive information about the item for sale. In practice, this means that a dealer has to provide information about the vehicle for sale as precisely as possible and also point out any deviations from the expected condition. Making statements about the manufacturer and model, age, and mileage should not be a problem. But how can the seller provide reliable information about the condition of the battery?

The innovative DEKRA rapid battery test only takes 15 minutes

One obvious solution would be to read out the SoH from the vehicle’s battery management system. Some manufacturers offer this option. However, these are so-called dry values which do not necessarily align with the real values. Expert organization DEKRA takes a different approach to assess battery health, allowing for an independent determination of the SoH. Patented in the beginning of November 2020 and validated by the renowned RWTH Aachen University, DEKRA rolled out its rapid battery test in December 2022. The test is based on a real measurement of the battery values on load and takes about 15 minutes. To do so, the tester initiates a test drive of a few hundred meters to achieve high battery performance through a short acceleration. Subsequently, the battery’s internal resistance is calculated. This is where the innovative aspect of the rapid test comes to play: a specially developed algorithm interprets the measured values correctly. Crucially, it relates and compares this data to a new vehicle, which serves as the necessary reference. In a sense, the used vehicle’s battery test begins with the test of a new vehicle of the same type.

During the initial inspection of new electric cars DEKRA also checks the batteries

The DEKRA Technology Center in Klettwitz is pivotal here. As part of an initial inspection, engineers thoroughly examine each individual electric vehicle type that is set to be tested in the future. A vehicle, equipped with extensive measuring equipment, is then driven on the test track for several days under different charging conditions and load intensities. This generates a wealth of data on the battery, which the algorithm for the battery test later uses as reference values. Once the used vehicle’s battery check has been completed, the tester issues a report containing the relevant vehicle data as well as the measurement data and the resulting State of Health.

The batteries of used electric vehicles are better than their reputation

DEKRA has now tested several thousand vehicles and has not yet found a single defective battery. “Overall, the batteries in electric cars are much better than their reputation. Our battery checks clearly support this,” reports Michael Tziatzios. So, what is the minimum SoH a used electric car should have for the new owner to enjoy it for longer? According to the DEKRA expert, a good SoH value generally lies between 80 and 100 percent. The higher the value, the better the health of the battery. And what if the battery only has a SoH of 75 percent? Even then, the car can still have a lifespan of several good years, especially when it is used primarily in city traffic.