Buying a used electric car in the UK – what the world’s biggest study found

Battery testing firm AVILOO has published results from more than 500,000 independent tests on used electric cars, showing battery health can vary by up to 13.5% between two examples of the same model.

The Austrian company released its AVILOO Certified EV Battery Report on Wednesday (2 September), calling it the largest independent study of used electric car battery health in the world.

The report covers 20 popular electric car models tested between 2022 and 2026 and draws on a wider AVILOO database of more than 1 million tests across North and South America, Europe, Australia and Asia.

AVILOO said every figure in the report comes from its own measurement rather than the car’s dashboard display, which varies between manufacturers and does not always reflect the true condition of the battery.

The firm said battery health across the used market remains robust overall, but the gaps between models and between individual cars are large enough to change what a vehicle is worth.

How the test works

The report uses AVILOO’s FLASH Test, a three-minute diagnostic that plugs into the car’s OBD port.

Rather than reading the value generated by the car’s own battery management system, the test calculates State of Health (SoH) using a statistical model trained on hundreds of thousands of comparable used cars, factoring in mileage, age, charging cycles, cell voltage and energy meter readings.

SoH is the percentage of the battery’s original usable capacity that remains, so a battery at 95% SoH still delivers around 95% of its original range per charge.

For each model, the report gives the median SoH at 50,000km (31,000 miles), 100,000km (62,000 miles) and 150,000km (93,000 miles), plus the band within which 99% of tested cars fell.

What the data shows

Across all 20 models, median battery health fell as mileage rose and the spread between individual cars widened with distance travelled. AVILOO said the differences between models held at all three mileage points.

At 50,000km, the spread between the healthiest and least healthy car of the same model ranged from 7.43 to 9.98 percentage points. By 150,000km, that spread had grown to between 9.42 and 16.39 percentage points.

AVILOO highlighted four models as examples of different battery sizes and vehicle types, stressing they are not a ranking:

• Tesla Model Y (78.8kWh): Median SoH of 94.5% at 50,000km falling to 90.3% at 150,000km, equal to real-world range dropping from around 379km to 362km. Individual cars deviated by up to 11% SoH, or around 46km of range per charge.
• Volkswagen ID.4 (77kWh): Median SoH of 95.3% at 50,000km falling to 90.6% at 150,000km, with range dropping from around 373km to 354km. Individual cars varied by up to 11% to 12% SoH at higher mileages, a difference of around 45km.
• Hyundai Ioniq 5 (72.6kWh): Median SoH of 97.2% at 50,000km falling to 92.8% at 150,000km, with range dropping from around 335km to 319km. The spread between cars grew to more than 12% SoH by 150,000km, around 42km of range.
• Nissan Leaf ZE1 (40kWh): Median SoH of 91.1% at 50,000km falling to 86.3% at 150,000km, the lowest of the four throughout. The spread reached 13.5% SoH at 150,000km, around 29km of real-world range, with median range falling from around 196km to 185km.

AVILOO said the Leaf’s battery is roughly half the size of the other three and needs charging far more often, which explains its faster degradation.

The firm added that cars with smaller batteries that need more frequent charging for the same distance tend to degrade faster than models with larger packs.

Climate and the used market

Temperature affects both how fast a battery ages and how well it charges, with batteries in cooler regions charging more slowly and wearing differently to those in warmer climates.

AVILOO said its global dataset gives a picture across all climate zones rather than the pattern of a single country.

“What this data really shows is that averages hide a lot. Yes, EV batteries age better than their reputation suggests, but that is not the most interesting finding,” said Marcus Berger, CEO of AVILOO.

Far more important is that battery health differs significantly between models, and even more so between individual cars of the same model, he said.

“Ten or fifteen percentage points of difference in State of Health means a real difference in range, value and reliability. Without an independent test, you simply do not know where your car sits in that range.”

“That is exactly why we developed the AVILOO FLASH Test, and exactly why this report is now published twice a year. We want to give the whole market, from private buyers to fleets and insurers, an honest, independent and truly global picture of how these batteries are holding up.”

Battery guarantee now available in the UK

AVILOO launched a battery guarantee across Europe this summer, covering the UK alongside Germany, Austria, Switzerland, the Netherlands, Finland, Belgium, Ireland, France, Sweden, Norway and Denmark.

For each car, the firm calculates a minimum SoH the battery must still reach after one year and 20,000km, and pays buyers €3,000 in most European countries if it falls short.

Mercedes-Benz, Volvo and Porsche Holding use AVILOO as their preferred independent battery testing partner across their European dealer networks, covering both their own vehicles and trade-ins.

Leasing firms Ayvens and Arval use the test for end-of-contract remarketing, auction houses BCA and Cox Automotive have built it into their European processes, and dealer groups Hedin and Emil Frey also use it.

AVILOO said it will publish the Certified EV Battery Report twice a year from now on.

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