EQA, IONIQ 5, and i4 Have Most Durable Batteries: Largest-Ever Independent Study on Used EV Battery Health Released

The largest independent study on used electric vehicle battery health to date has been published: Mercedes-Benz's EQA, Hyundai's IONIQ 5, and BMW i4 rank top three for battery state-of-health (SoH) after 150,000 km of use — at 94.0%, 93.8%, and 93.6% respectively — significantly outperforming most rivals in their segments.

The report was released by Austrian battery diagnostics firm AVILOO, using its FLASH testing system to conduct physical-level battery assessments across over 500,000 used EVs in Europe, North America, South America, Australia, and Asia. It covers 20 mainstream models, with individual vehicle tracking extending up to 150,000 km (~93,000 miles). SoH — the percentage of current usable battery capacity relative to original nominal capacity — directly correlates with real-world driving range: a 94% SoH means the vehicle retains approximately 94% of its factory-rated range.

Data shows the IONIQ 5 excels especially at low mileages: its SoH reaches 97.1% at 50,000 km — the highest across all models. As mileage increases, the EQA and i4 overtake others thanks to more stable degradation curves. Hyundai's Kona EV and Volvo XC40 Recharge follow closely, both maintaining SoH above 92.7% after 150,000 km. In contrast, TeslaModel 3 ranks second-to-last at 88.9%, while Model Y sits at 90.3% — below leading German models but still within industry-acceptable limits.

The study also notes that vehicles with smaller battery packs tend to degrade faster: the Nissan Leaf ZE1 (86.7%), MINI Cooper SE (87.1%), and Renault Zoe (87.3%) rank lowest — primarily because ~40 kWh batteries require more frequent charge/discharge cycles to achieve equivalent mileage, accelerating aging. Notably, AVILOO's earlier dedicated test on lithium iron phosphate (LFP) batteries found that Tesla models equipped with LFP cells exhibited better degradation control than nickel-based Model 3 variants.

The report stresses that median SoH values serve only as statistical references — inter-individual SoH variation within the same model can reach up to 13.5 percentage points, translating to tens of kilometers of real-world range difference. Moreover, SoH values displayed on vehicle dashboards lack cross-brand comparability due to inconsistent OEM algorithms. Therefore, relying solely on spec sheets or dashboard readouts is insufficient when evaluating battery condition in used EVs; professional third-party testing is increasingly essential.

AVILOO's FLASH test connects via the vehicle's OBD port and calculates SoH using a statistical model trained on millions of real-world vehicle data points — bypassing limitations of automaker-supplied BMS self-reporting. The methodology is certified by TÜV and CARA and has been designated the preferred independent battery testing solution for authorized dealers of Mercedes-Benz, Volvo, and Porsche. This summer, the company also launched battery warranty services across 12 European countries, guaranteeing up to €3,000 compensation if the battery's SoH falls below an agreed threshold within one year.