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Used electric cars are difficult to sell. Because its heart, the battery, poses a mystery to prospective buyers. The industry wants to provide insight with battery checks. But how?
With a combustion engine, a test drive and a look under the hood can at least indicate how the previous owner handled the vehicle. In contrast, the most expensive component of an electric car is a “black box” that hides its interior: the ions – those electrically charged particles that provide power – may have been transported through the landscape by the previous owner in a feel-good atmosphere. Or he kicked them so that the battery cell walls bend.
Combustion and electric cars share the same fate: their driver. Extreme actions such as long periods of driving under full load or long periods of idle time under incorrect conditions cause both to age equally.
Daniel Görges researches electromobility at the Rhineland-Palatinate Technical University of Kaiserslautern-Landau. The good news: “Practical experience shows that the durability of electric car batteries is greater than many experts expected.” And the vehicle itself takes care of much of what concerns the battery’s well-being.
Fast charging puts a lot of strain on the battery
There are only a few things that electric car drivers have to pay attention to themselves: “You shouldn’t always charge fully; in many models this can be prevented through settings.” This requires more planning than with a combustion engine: “If I know that I don’t need the full range on the next trip, then the next charging process should be limited to 80 percent.” The battery always feels most comfortable when it is half full. “Below 20 percent is not good either,” advises Görges, “because then electrochemical processes occur in the battery that are unfavorable for its service life.”
Even when it comes to charging itself, the battery likes it leisurely: “Up to eleven kilowatts, typical for wall boxes and normal charging stations, is not critical when it comes to aging,” says Görges. “Fast charging, on the other hand, with 50 kilowatts or more puts a lot of strain on the battery. If you don’t need that, you should avoid it.” The smaller the state of charge changes, the better.
But did the previous owner take all of this to heart? Two thirds of new cars in Germany are registered as fleet or company cars and sold comparatively quickly as used cars. “For the original owner, the issue of battery life is therefore unimportant,” says Görges. For used car buyers, however, health is a very important issue.
“Health certificate” only of limited significance
The industry has also recognized this – at least since used electric cars turned out to be not exactly a hit with car dealers. In addition to the higher price, the “battery pig in a poke” is also frightening.
An unusually long guarantee, especially for cars from German manufacturers, is intended to create trust: in many cases the battery should still have at least two thirds of its remaining capacity after eight years or 160,000 kilometers. Some manufacturers even offer a ten-year or up to one million kilometer guarantee.
Battery test reports are intended to help, among other things, when buying a used electric car. However, their significance is limited.
They also refer to “battery health certificates” or “State of Health” tests, or SoH for short. It is a buyer-friendly tool that combustion engine drivers can only dream of: “It uses a measurement method in which the available battery energy content, or the ‘state of health’, is read,” explains Jochen Tekotte, spokesman for sustainability at Volkswagen.
However, he has to limit the informative value of the offer a little: “Since the basic parameters are not known at the time of determination – such as temperature, charging speed – the measurement accuracy cannot be guaranteed.” A VW dealer’s “Battery Health Quick Test” says: “The result of the measurement can deviate from the actual remaining capacity by up to plus or minus ten percentage points.”
Measured values pose puzzles
That’s sobering. Experts advise used car buyers to stay away from electric vehicles with an SoH of less than 80 percent. This limit is now shifting with the measurement uncertainty. The test sheet is therefore “de facto worthless,” says Marcus Berger.
He is an expert in the field of battery diagnostics and head of AVILOO, a battery testing provider. The experience he gained doesn’t exactly strengthen confidence in the used electric car market: “We’ve already had vehicles where the SoH was around 40 percent and the battery management system still showed it in the 90 percent range.”
Even if the information is correct, its interpretation is likely to puzzle consumers: harmful fast charging processes are hidden under “proportion of DC charged energy”; Battery wear reveals the total “charged energy in kilowatt hours” by dividing its value by the total capacity of the traction battery – but please without the buffer that the manufacturer may have set up to protect the battery. And don’t forget the “cell voltage spread”!
Görges agrees that such data sheets are difficult for most people to understand. “It should be broken down into a few, crucial pieces of information that are easy to understand and understand. Exact measurements are only helpful for experts.”
Evidence must be comparable
Used car dealers also see battery trials and tribulations, but they don’t yet have a solution. “We are currently looking at the various test providers for high-voltage batteries in order to be able to offer our member companies an industry solution,” says Marcus Weller, electromobility coordinator at the Central Association of the German Motor Vehicle Trade. Because he also sees: “A meaningful battery check can remove some of the skepticism towards used electric vehicles.”
Consumer advocate Gregor Kolbe, transport market expert at the Federal Association of Consumer Organizations, also thinks so. “Since an electric car battery cannot be tested from the outside, the SoH certificates are so important. However, they must be comparable.” There is a need for uniform testing procedures that also enable the comparison of e-vehicles from different manufacturers: “Manufacturers and dealers should have an interest in offering meaningful and comparable SoH certificates,” says Kolbe.
Automobile clubs are now also trying to support their members. “To do this, a small diagnostic device is connected to the car and the battery has to be driven largely empty once,” explains ADAC spokesman Micha Gebhardt. The collected data is then evaluated and a battery certificate is issued.
The ADAC is working with Berger’s company. But its certificates still have room for improvement: the SoH value is immediately visible and, according to Berger, the measurement tolerance is just one percent for 99 out of 100 cars. However, there is no information about fast charging processes or downtimes.
Database still too narrow
Berger gives a good reason why consumer-friendliness leaves something to be desired: the database. Because if only a few battery test results are available for a model, the individual result – is it particularly good in comparison or not? – not classifying it clearly enough. “However, we have developed this necessary database over the last year with over 50,000 battery tests carried out. We are therefore currently revising the Aviloo battery certificate.”
The electric car still requires the industry and its customers to do some homework. For good reason, as the managing director of the “Allianz Center for Technology” Christoph Lauterwasser says: “We have more than 125 years of experience with combustion engines, but only around ten years with modern electric vehicles.”