Why Your Electric Car Battery Is Almost Certainly Healthier Than You Think

One of the biggest barriers to buying an electric car has always been the fear of what happens to the battery. Will it deteriorate quickly? Will you be left with a car that barely makes it around the block after five years? Will resale values collapse because no buyer will touch an old EV with a degraded battery? A major UK study published in February 2026 has now produced the most detailed answer yet to all of these questions, and for almost every EV owner, the answer is far more reassuring than the narrative that has surrounded electric car batteries for the past decade.

The Generational Battery Performance Index, compiled by London-based company Generational and covering 8,000 electric vehicles from 36 different brands, found an average battery state of health of 95 percent across the entire sample. To put that in practical terms: the average EV battery, across the full age and mileage range of the study, is performing at 95 percent of its original specification. The cars included everything from brand-new vehicles to those up to 12 years old with over 160,000 miles on the clock.

What the Study Actually Found

Battery state of health (SoH) is the measure used to describe how much of a battery’s original capacity it retains over time. A brand-new battery has a state of health of 100 percent. A battery that has lost ten percent of its original range has a state of health of 90 percent, meaning a car rated for 250 miles of range would now deliver approximately 225 miles. The threshold at which most manufacturers trigger a warranty replacement is 70 percent SoH.

The Generational study found that the average SoH across all 8,000 vehicles in the dataset was 95 percent, which is well above the level that most consumers fear and significantly higher than the 70 percent warranty trigger. Even more telling was the performance of older vehicles. Among EVs aged between eight and 12 years, the median battery health sat at 85 percent, with the lower quartile averaging 82 percent. The best-maintained cars in that age bracket were still operating at around 90 percent of their original capacity.

High Mileage Does Not Mean High Degradation

Perhaps the most practically useful finding for drivers considering a used EV purchase is the data on high-mileage vehicles. Cars with over 100,000 miles recorded battery state of health figures between 88 and 95 percent. This directly contradicts the assumption, widespread in the used car market, that high mileage is a reliable proxy for battery degradation in electric vehicles.

Mileage alone, the study concluded, is not a reliable predictor of battery condition. A 100,000-mile EV that has been driven predominantly on motorways at moderate speeds, charged regularly but not exclusively at fast chargers, and garaged in moderate temperatures will typically have a healthier battery than a lower-mileage car that has been repeatedly fast-charged in extreme temperatures and left for long periods at very low or very high states of charge.

Oliver Phillpott, chief executive 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 percent, and even older vehicles comfortably exceeding warranty thresholds, the underlying fundamentals are extremely strong.”

He continued: “Transparency in battery condition is the main challenge facing the market today, and essential infrastructure for a healthy used EV sector. As vehicles age, the variance between the best and worst performers widens, and that dispersion defines risk. By establishing clear benchmarks for what is typical, above and below average, we are giving the market the reference points it needs to price risk accurately, strengthen residual values and accelerate adoption.”

Why People Feared Battery Degradation So Much

The concern about electric car battery longevity has always had some basis in reality, but that basis has been significantly overstated in public discourse. Early-generation EVs, particularly the first and second-generation Nissan Leaf models, were built with passive battery cooling systems that left cells more vulnerable to temperature extremes. In hotter climates or in cars left outdoors in summer heat, degradation was faster and sometimes severe. Some first-generation Leaf owners in the American South reported losing a third of their range within five years.

Modern EVs use active liquid cooling and heating systems that maintain cells within an optimal temperature range regardless of external conditions. Every mainstream electric car sold in the UK since approximately 2019 uses this approach. The result is a fundamentally different degradation profile from the first generation, and the Generational study’s data reflects this. As the study notes, even the oldest vehicles in the dataset, which include some early liquid-cooled models, are performing at median levels well above public expectations.

Battery warranties have also become considerably more generous. Most manufacturers now cover the battery to at least 70 percent SoH for eight years or 100,000 miles, whichever comes first. Several brands, including Kia, Hyundai, and Genesis, have extended their battery warranties to 10 years or 150,000 miles as standard. If a battery falls below the warranty threshold within that period, the manufacturer is required to repair or replace it at no cost to the owner.

What This Means for Buyers and Owners

For anyone considering buying a used electric car, the Generational data provides a useful calibration point. The average used EV battery is performing at 95 percent of its original specification. Even in the oldest and highest-mileage vehicles in the study, the median was 85 percent and the lower quartile was 82 percent. A car delivering 82 percent of its rated range is still a fully functional vehicle for most daily use cases, and the vast majority of used EVs are performing considerably better than that.

When viewing a used EV, ask the seller or dealer for a battery health report. Several independent companies, including Generational itself, offer battery state of health checks that provide a verified figure in percentage terms. Some manufacturers, including Tesla, allow potential buyers to run a battery health check through the car’s software before purchase. Others, such as Volkswagen and BMW, have dealer-level diagnostic tools that can produce a state of health report on request.

For current owners, particularly those with older or higher-mileage EVs, the data suggests your battery is almost certainly in better shape than you might have assumed. The best way to preserve battery health over the long term is to avoid regularly charging to 100 percent unless a long journey requires it, avoid leaving the battery at very low states of charge for extended periods, and use DC rapid charging only when necessary rather than as a routine approach. Home charging on a standard 7kW wallbox overnight, typically to around 80 percent, is the approach most consistently associated with long-term battery health in the research literature.

The Generational study is the first in a series of annual Battery Performance Index reports, and Phillpott indicated that the company will track how state of health figures change across the fleet as more data is collected each year. For a market in which battery anxiety has been one of the primary objections to electric vehicle adoption, accurate, data-driven benchmarks of this kind are the most direct way to close the information gap between what drivers fear and what the evidence actually shows.

For more on the costs and practicalities of EV ownership, see our guide to why public EV charging is now cheaper per mile than petrol for the first time.

Sources:

• EV car batteries last longer than expected, according to new study – RAC Drive
• The closing longevity gap between battery electric vehicles and internal combustion vehicles in Great Britain – NCBI
• Used EV batteries last longer than many expect – Drive Electric