The Largest EV Battery Study Yet Shows Two Identical Cars Can Age Very Differently

If you’re shopping for a used EV and going by the battery health percentage on the listing, that single number is telling you less than you’d think. Austrian diagnostics company AVILOO has just published what it calls the largest independent study of used EV battery health ever done, and the headline finding cuts both ways: batteries are holding up better than most people assume, but two examples of the exact same model can age very differently from each other.

The AVILOO Certified EV Battery Report draws on more than 500,000 physical battery measurements collected between 2022 and 2026, across 20 popular EV models sold in Europe, North America, South America, Australia and Asia. Every reading comes from AVILOO’s own FLASH Test, a three-minute diagnostic run through the car’s OBD port, because dashboard percentages vary between manufacturers and don’t always reflect what’s actually going on with the battery.

What the data actually shows

AVILOO calculated the median State of Health, the share of a battery’s original usable capacity still available, at three mileage points: 50,000km, 100,000km and 150,000km. Most models held up well past the point owners tend to worry about, with the Mercedes-Benz EQA topping the results at 96.6% SoH at 50,000km and still 94.0% at 150,000km.

Tesla Model Y, the Volkswagen ID.4, the Hyundai IONIQ 5 and the Nissan Leaf ZE1 were singled out to illustrate the range of battery sizes in the study.

The Leaf’s smaller, air cooled battery has to cycle far more often to cover the same distance as the other three, and its chemistry doesn’t do it any favours either: older NMC cells like the ones in the Leaf tend to wear faster than the LFP packs many newer budget EVs now use, something I’ve broken down in my comparison of LFP and NMC battery chemistry. Between the two, it’s no surprise the Leaf posted both the lowest median health and the widest spread of any model AVILOO tested.

Why the spread matters more than the average

An 11 to 13.5 percentage point gap sounds abstract until you turn it into range. At 150,000km, that spread works out to roughly 29km separating the healthiest and weakest Model Y in the study, and around 42km for the IONIQ 5. Over a normal week of driving, that’s easily enough to turn a trip you’d normally do without thinking into one where you’re hunting for a charger halfway there.

What is State of Health (SoH) in an EV battery?
SoH is the percentage of a battery’s original usable capacity that remains. A battery at 90% SoH still delivers roughly 90% of the range it offered when new, though other factors like driving style and temperature also affect real world range.

AVILOO’s CEO Marcus Berger made the point simply: you can’t know where your own car actually stands until you test it. The model average is a fine starting point, but it says nothing about the specific car in front of you, and the gap between the best and worst examples just keeps growing the more miles go on the clock.

Who’s already using this

Some big names are treating this as standard practice, not just a nice extra. Mercedes-Benz, Volvo and Porsche Holding have all made AVILOO their go to independent tester for dealership stock, and firms like Ayvens, Arval, BCA, Cox Automotive, Hedin and Emil Frey use the same FLASH Test to check used cars before they go up for sale.

AVILOO has also backed its own data with money. Its Battery Warranty, now live across 12 European countries, guarantees a minimum SoH threshold at 20,000km within a one year period, with payouts of up to €3,000 (US$2,600) if a car falls short. It’s a fairly direct way of putting the company’s confidence in its own testing where its mouth is.

This isn’t the only study finding the same gap. UK firm Generational looked at used EVs separately and found that around 1 in 85 has a hidden cell level imbalance that a standard SoH reading won’t catch, since it never shows up as a dashboard warning even though it can affect range and charging. Put the two studies together and the message is simple: one SoH number, wherever it comes from, doesn’t tell you enough on its own.

Now that doesn’t mean EV batteries are a gamble. If anything, the AVILOO data is reassuring: most models are still comfortably above 90% health at 150,000km, well past what most owners will ever drive. The real takeaway is narrower and more useful than that: if you’re buying used, ask for an independent test on the specific car, not the model average, because at higher mileage that’s increasingly where the real difference sits.

FAQ

Can I trust the battery health percentage shown on an EV’s dashboard?
Not entirely. AVILOO says dashboard readings vary between manufacturers and don’t always reflect a battery’s true condition, which is why its own FLASH Test relies on physical measurement through the car’s OBD port instead.

Which EV manufacturers use AVILOO’s battery testing?
Mercedes-Benz, Volvo and Porsche Holding have each selected AVILOO as their preferred independent battery testing provider for European dealerships, alongside leasing firms Ayvens and Arval and dealer groups including Hedin and Emil Frey.

How much can EV battery health vary between cars of the same model?
AVILOO’s study found a spread of up to 13.5 percentage points in State of Health between individual examples of the same model at 150,000km, with the Nissan Leaf ZE1 showing the widest gap of the models detailed in the report.

Do EV batteries actually hold up well over time?
Yes, generally. AVILOO’s data shows most of the 20 models studied retained more than 90% of their original battery capacity at 150,000km, with the Mercedes-Benz EQA topping the results at 94.0%.

Featured Image: Aviloo