Study: EV Batteries Retain Over 85% Health After 8+ Years

UK-based battery diagnostics firm Generational recently released its "2025 Battery Performance Index" report, based on real-world testing data from over 8,000 electric vehicle (EV) batteries. The study found that the median state of health (SoH) for batteries in vehicles older than eight years remains at 85.04%—significantly higher than industry expectations. The research covered 36 brands of battery electric vehicles (BEVs) and plug-in hybrid electric vehicles (PHEVs), spanning model ages from zero to 12 years and with odometer readings as high as 257,000 kilometers. Data showed that the average SoH across all sampled batteries was 95.15%. Even for older batteries aged 8 to 12 years, the 25th percentile SoH reached 82%, while the 75th percentile was as high as 90%—substantially exceeding the typical manufacturer warranty standard of 70% capacity retention after eight years or 160,000 kilometers. The report also noted that battery degradation is not a systemic risk and that mileage alone is not a reliable predictor of battery health. Instead, usage patterns and environmental conditions have a greater impact on battery condition. The findings suggest that the service life of most EV batteries today is already equivalent to—or even exceeds—the typical vehicle ownership period.