UK Cars
Battery Health and Longevity: What the Data Actually Says About How Long EV Batteries Last
The biggest UK battery health study found an average state of health of 95%. Here is what real degradation data says about how long an EV battery really lasts.
Ask a room of drivers what puts them off electric cars and the battery comes up quickly. Not the price, not the charging, but the worry that the most expensive component in the car will fade away years before the rest of it is finished. It is a reasonable fear on paper: a traction battery is a lump of chemistry, chemistry ages, and replacing one out of warranty is expensive. The interesting thing is what happens when you swap the fear for the field data. Two large studies published in the last eighteen months, one from each side of the Atlantic, point the same way, and the numbers are more reassuring than most buyers expect.
The UK's biggest battery health study
The most useful evidence comes from close to home. Generational, a London-based EV battery diagnostics firm, analysed battery assessments from more than 8,000 UK electric cars and light commercial vehicles across 36 manufacturers, with vehicle ages from new to 12 years and mileages up to and beyond 160,000 miles. The headline figure: average battery state of health across the whole dataset stands at 95.15% of original capacity. On a typical 60kWh pack that is a loss of around 3kWh, the difference between a 250-mile range and a 238-mile one. Noticeable on a spreadsheet, invisible on most journeys.
The age breakdown is where it gets more interesting. Among four- to five-year-old cars, the median state of health is 93.53%, with even the bottom-performing quartile sitting at 91.64%. Move up to the eight- to 12-year-old cohort, cars built in the mid-2010s when battery management systems were cruder, and the median is still 85.04%. The bottom quartile in that group is 82%. Compare all of those with the threshold most manufacturers use, and the gap is enormous.
That threshold matters because it defines what the industry itself considers a problem battery. Most brands warranty the pack for 8 years or 100,000 miles, committing to restore or replace it if capacity falls below 70% of the original figure, and the warranty transfers to subsequent owners. Generational's finding is that even decade-old packs are comfortably clearing a bar the industry set for batteries a third of their age. High-mileage cars tell a similar story: vehicles with more than 100,000 miles on the clock frequently return state-of-health readings of 88-95%.
The telematics view
The second dataset comes from Geotab, the telematics firm, which has been running the same analysis for years and updating it as the fleet matures. Its 2026 study, published in April, covers more than 22,700 vehicles across 21 models and finds an average degradation rate of 2.3% per year. On that trajectory the average battery reaches about 81.6% of its original capacity after eight years, again clearing the 70% warranty line with room to spare.
The number deserves a little context, because it has moved around. Geotab's 2020 study found the same 2.3% average. A 2023 re-run on 11 common models found an improved 1.8%. The latest, wider dataset has settled back at 2.3%, and Geotab's own reading is that this reflects a changing fleet rather than worse batteries: the sample now includes newer generations of cars and, importantly, far more reliance on rapid charging. The batteries are not getting worse; the way we use them is shifting.
What actually wears a battery out
This is where the research earns its keep, because it replaces old advice with evidence. The single largest stressor in Geotab's data is high-power DC fast charging above 100kW, which pushes degradation rates to up to twice those of the low-power charging group, 3.0% versus 1.5% per year. Heat is the second factor: cars run in hot climates degrade about 0.4 percentage points faster per year than cars in mild ones, which is quietly good news for a UK fleet that spends its life in a mild, damp climate.
The most myth-busting finding concerns daily habits. For most EV use, Geotab found no need to worry about fully charging or fully emptying the battery. Degradation only accelerates when a car spends more than 80% of its time parked at or near full or near empty. The owner who charges to 100% the night before a long trip and runs the pack down on the motorway is doing the battery no harm at all. The one to watch is the car that sits at 100% for days on end, or one that is habitually run to almost nothing and left there. Otherwise, charge it, drive it, and stop thinking about it.
What this means when you are buying
The practical takeaway splits neatly by buyer. If you are buying new, the warranty does most of the work: eight years and 100,000 miles of cover against falling below 70% capacity, transferable when you sell, is a long runway, and the data says most packs will never come near claiming on it.
If you are buying used, the message is that age and mileage are blunt instruments. Generational found that mileage alone is an increasingly unreliable indicator of battery condition, with younger high-mileage cars frequently outperforming older low-mileage ones. That turns the used-market question from "how old is it?" into "what does the battery test say?", which is why battery health certificates are becoming standard practice on manufacturer approved-used schemes and why independent testing is spreading. A verified state-of-health reading is worth more than the odometer, and we cover the buying checklist in more detail in our guide to the used EV market.
None of this means batteries never fail. Packs do degrade, variance between individual cars grows with age, and a small number will underperform. But the wholesale replacement scenario that sits at the back of many buyers' minds is not what the data shows. It shows a component that, in the vast majority of cases, is likely to outlast the car around it.