The UK’s largest study of used electric vehicles has found that battery degradation may be far less severe than many drivers and industry observers assume.
Battery diagnostics specialist Generational analysed more than 8,000 electric cars and light commercial vehicles, assessing battery state of health, SoH, across 36 manufacturers. The findings, published in its 2025 Battery Performance Index, offer fresh insight into how age and mileage affect EV battery degradation rates.
Strong retention even at 8 to 12 years
The study found:
- 4 to 5 year old EVs show a median battery SoH of 93.53%
- 8 to 9 year old vehicles retain a median 85% capacity
- The overall fleet average SoH was 95.15%
- High mileage EVs, 100,000 miles plus, frequently returned 88 to 95% SoH
Most manufacturers warranty batteries to at least 70% SoH for eight years or 100,000 miles, whichever comes first. Generational’s data suggests the vast majority of vehicles significantly outperform this threshold.
However, the research also highlights that as vehicles age, the gap between the best and worst performers widens. In the 8 to 12 year cohort:
- 25th percentile sat at 82% SoH
- Median was 85.04%
- 75th percentile reached 90%
This growing variance underlines why individual battery assessment is becoming more important than headline averages.
Mileage is not the whole story
One of the most notable conclusions is that mileage alone is an unreliable indicator of battery condition.
In some cases, a three year old fleet car with 90,000 miles showed stronger battery health than a six year old vehicle with just 30,000 miles. Charging patterns, duty cycle and usage appear to play a greater role in EV battery degradation rates than simple mileage figures.
For driver trainers considering switching to electric, or advising pupils and fleet clients, this reinforces the importance of understanding battery health data rather than relying on assumptions inherited from the internal combustion era.
Implications for trainers and fleets
For ADIs and PDIs running electric tuition vehicles, the findings are reassuring. High annual mileages typical of training vehicles do not automatically translate into severe battery degradation.
For fleet trainers and those involved in grey fleet or corporate driver training:
- Verified battery testing can strengthen residual values
- Accurate SoH data supports total cost of ownership calculations
- Holding periods can be planned with greater confidence
As used EVs increasingly enter the training market, battery transparency may become as fundamental as service history or mileage checks.
Philip Nothard, chair of the Vehicle Remarketing Association, said buyers place “a huge emphasis on battery health” and that transparency will be crucial in dispelling misconceptions around EV batteries.
Supported by wider research
The findings echo a separate large scale analysis by Geotab, which examined more than 22,700 EVs across 21 makes and models. That study reported an average annual battery degradation rate of 2.3%, compared to 1.8% the previous year.
Together, the research suggests that while EV battery degradation rates are real and measurable, they are not the systemic risk once feared.
For the instructor community, this may help address one of the most persistent concerns raised by learners and parents considering electric vehicles: battery longevity.
As the used EV market matures, independent battery health verification looks set to play a central role in pricing, confidence and long term adoption.
Source via: Fleet News
