Generational, a UK-based developer of electric vehicle (EV) battery condition diagnostics, has launched its
2025 Battery Performance Index. The ‘largest analysis of electric vehicle battery condition undertaken in the UK’, it showed that the average battery ‘state of health’ (SoH) across more than 8,000 tested passenger cars and light commercial vehicles was a ‘robust 95.15% of capacity compared to new’.
Generational says its Index establishes clear benchmarks for what can be considered typical, above-average and below-average battery degradation in UK vehicles moving through 2026, adding that it provides a new reference point for consumers and the industry across retailers, fleet operators, insurers and financiers.
Based on battery assessments conducted across 36 manufacturers, vehicle ages from 0-12 years, and mileages from 0 to more than 160,000 miles, Generational’s data shows: an overall average SoH of 95.15%; that eight- to nine-year-old vehicles retain a median 85% capacity; that high-mileage EVs (100,000-plus miles) frequently return 88-95% SoH; that even within the four to five-year cohort, the median SoH remains strong at 93.53%; and that OEM warranty thresholds (typically 70% SoH over eight years/100,000 miles) are rarely approached.
The index also breaks down into percentile benchmarking by vehicle age. For example: among four- to five-year-old vehicles, ‘the 25th (bottom-performing) percentile’ sits at 91.64% SoH, the median at 93.53%, and ‘the top-peforming 75th percentile’ at 96.49%; and that in the eight- to 12-year-old cohort, the 25th percentile is 82%, the median 85.04%, and 75th percentile 90%.
Averages remain strongGenerational said: “This widening spread with age shines a sharp spotlight on how, while averages remain strong, variance increases materially over time, creating a growing performance gap between well-maintained vehicles and under-performers. The data also confirms that battery degradation is not the systemic risk once assumed, with uncertainty around condition now the principal determinant of used EV confidence, residual values, performance and risk.
“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.
“What the findings mean for consumers is that in the vast majority of cases, EV batteries are likely to exceed the lifespan of the vehicle itself. Even vehicles approaching the end of typical OEM battery warranty periods are performing comfortably above minimum thresholds. However, the increasing dispersion of performance over time underlines why verified battery testing is becoming essential. Without transparent condition data, worst-case assumptions can dominate pricing and decision-making.”