Battery testing firm Generational has published the 2025 Battery Performance Index, looking at how batteries perform over time.
Drawing on battery assessments conducted across 36 manufacturers, vehicle ages from 0-12 years and mileages from 0 to over 160,000 miles, it found that the overall average state of health (SOH) was 95.15%.
Eight-to-nine-year-old vehicles retain a median 85% capacity, high-mileage EVs with 100,000+ miles on the clock return 88-95% SoH. For 4-5-year cars, median SoH remains strong at 93.53%.
In the 8-12-year-old cohort, the 25th percentile is 82%, median 85.04%, and 75th percentile 90%.
The new Index also demonstrates that mileage alone is an increasingly unreliable indicator of battery condition.
In many cases, younger high-mileage vehicles outperform older low-mileage equivalents, challenging traditional appraisal models inherited from the internal combustion era.
A three-year-old fleet vehicle with 90,000 miles may represent a stronger battery proposition than a six-year-old vehicle with 30,000 miles, depending on usage and charging behaviour.
Oliver Phillpott, CEO of Generational, said: “The Generational Battery Performance Index definitively shows that EV batteries are performing far better than many consumers and industry stakeholders have been led to believe.
“With an average State of Health of over 95%, and even older vehicles comfortably exceeding warranty thresholds, the underlying fundamentals are extremely strong.
“By establishing clear benchmarks for what is typical, above and below average as we look to drive further growth in 2026, we are giving the market the reference points it needs to price risk accurately, strengthen residual values and accelerate adoption.”
