A massive analysis of more than 500,000 EV battery tests suggests that most electric cars retain at least 90% of their original battery capacity after 150,000 kilometers.

But the averages hide large differences between individual cars – precisely why Belgium is already adding battery-health data to the Car-Pass and why calls for an independent battery certificate for used EVs are growing in Belgium and the Netherlands.

Austrian battery-diagnostics specialist Aviloo analyzed more than 500,000 of its FLASH tests conducted between 2022 and 2026 across 20 popular EV models. They form part of a worldwide database exceeding one million tests.

For each model, Aviloo calculated the median State of Health (SoH) at 50,000, 100,000 and 150,000 kilometers. The results suggest that fears of EV batteries being exhausted after only a few years are largely misplaced.

At 150,000 km, a Mercedes EQA still averages almost 94% of its original capacity. Hyundai’s Ioniq 5, the BMW i4, Volvo XC40 Recharge, and several other models also remain above 90%.

Tesla’s figures remain respectable too. Aviloo puts the Model Y at around 90% after 150,000 km, while the Volkswagen ID.4 with its 77-kWh battery reaches roughly the same level. Older models with smaller batteries fare somewhat worse: the Nissan Leaf ZE1 with its 40-kWh pack drops to around 86%.

Same mileage, very different battery

However, turning those numbers into a simple ranking of the ‘best’ EV batteries would miss the study’s most significant finding. Differences between individual examples of the same model become considerably wider as mileage increases.

Among cars with around 150,000 km, battery health can differ by more than ten percentage points even between otherwise similar vehicles. Aviloo found a spread of more than 12 points for the Ioniq 5 and around 13.5 points for the Nissan Leaf, as highlighted in its report. Some model distributions across the complete dataset are wider still.

That means that two five-year-old EVs of the same model and with the same mileage could have significantly different usable ranges – and arguably deserve different second-hand prices.

Mileage, age, and maintenance history have traditionally been among the main indicators of a used car’s condition. With an EV, the health of the battery is increasingly becoming another crucial parameter.

Belgium puts SoH on the Car-Pass

That issue is particularly topical in Belgium. Since 1 January 2026, sellers of second-hand BEVs and plug-in hybrids can voluntarily have an independent State of Health (SoH) test added to the Car-Pass. The SoH percentage and underlying test information can consequently accompany the obligatory mileage history when the car is sold.

Car-Pass wants to go further and has advocated making battery-health information mandatory for electric and plug-in hybrid cars with sufficiently large batteries. It also eventually wants car manufacturers and importers to provide SoH data from connected vehicles automatically.

Flanders is meanwhile examining a brand-independent SoH test that could be offered alongside the future voluntary inspection of used cars and potentially during periodic technical inspections. A legal framework is still required.

The Netherlands does not yet have an equivalent compulsory battery certificate. However, both BOVAG and the Vereniging Elektrische Rijders have been pushing for reliable, uniform battery-health information for second-hand EV buyers.

Interestingly, an earlier Dutch comparison involving 185 test rounds on 24 brands and models rated Aviloo’s FLASH test and rival Moba among the most reliable of five independent testing systems examined. That provides useful external backing for Aviloo, although its new half-million-test analysis requires one important qualification.

Independent, but not academic

Aviloo is an established Austrian battery diagnostics specialist whose technology is also used by or recognized by organizations including Germany’s ADAC and Austria’s ÖAMTC. Its FLASH test connects through a car’s diagnostic port and analyses parameters such as age, mileage, charging history, cell-voltage differences, and energy counters against Aviloo’s extensive database. It therefore goes further than simply reading the State of Health number provided by the manufacturer’s battery-management system.

But this is not a peer-reviewed academic study. Aviloo collected the test data, developed the algorithms, analyzed the results, and published the report. It also earns money from battery tests and certificates, the usefulness of which the findings underscore.

Aviloo’s description of its report as the “world’s largest independent EV battery study” should therefore be interpreted as independent of the vehicle manufacturers, rather than independent scientific research into Aviloo’s technology.

Battery certificate could become the new odometer

Nevertheless, the dataset’s size makes its central message difficult to ignore. EV batteries appear to degrade substantially more slowly than many consumers still fear, with even high-mileage cars typically retaining a large majority of their original capacity. At the same time, averages are becoming less useful when assessing an individual second-hand EV.

That is particularly important in Belgium and the Netherlands, where the large wave of electric company and lease cars sold over the past few years is increasingly entering the used-car market. For those cars, knowing that an EV has driven 120,000 or 150,000 kilometers may no longer be enough. A verified battery-health certificate could become almost as important to its value as the odometer reading itself.