EVs are practically worthless secondhand, because the huge batteries will need expensive replacement after a few years. At least, that’s what somearticles or forum discussions in recent years may lead you to believe. However, while secondhand prices for EVs have been plummeting, evidence is building that their batteries could last longer than the eight-year warranties most come with. In fact, they could still be very usable even after 20 years, potentially giving full-electric cars a longer useful life than many fossil-fuel equivalents.

“There is an immense amount of consumer concern around the state of the battery that you buy in a secondhand vehicle,” says James Wallace, cofounder of Fortescue’s battery intelligence division Elysia. His company, formerly Williams Advanced Engineering prior to the Fortescue acquisition, has been developing software to optimize battery performance in intensive-use situations such as motorsport (including Formula E), mining, and for automaker JLR. Wallace is hoping Elysia’s technology will filter down to the mainstream, to help “give consumers more transparency on the secondhand batteries that they buy.”

People base assumptions on existing experience. When it comes to battery longevity, that’s mostly likely going to be their smartphones. Most of us see the battery life of our handsets start to drop after a couple of years. Apple’s Batterygate likely won’t have helped with the popular image of the durability of lithium-ion cells, either.

Built to Last

But there is growing indication that EV batteries are much sturdier than those in smartphones. Just for starters, you don’t tend to recharge your EV every day like your handset. It might be as infrequently as once a week or less. Real-world studies show how this affects an electric car’s battery. Consulting firm P3 recently analyzed 7,000 fleet electric vehicles, in partnership with Austrian battery testing specialist Aviloo. Their report showed that, on average, EV batteries have 90 percent capacity after 100,000 kilometers of driving, and at 300,000 kilometers they still have 87 percent of their original kilowatts left.

Similarly, data from fleet telematics company Geotab has revealed that battery depletion is much lower than originally predicted over time. While the P3 research is based on vehicles between three and five years old, mapping remaining battery capacity against mileage, the Geotab analysis looks at age. “We did a study in 2019, and then we did a more recent study as well,” says Charlotte Argue, senior manager for sustainable mobility at Geotab. “The most recent study was 11 different models and brands. Our 2019 study included 23 different models with multiple generations.”

In both these reports, Geotab was tracking the state of charge and measuring the energy flow of the vehicle in use, which was also the approach taken by P3 and Aviloo. “Using that we can estimate at any given time what the total battery capacity is in that vehicle's life,” says Argue. “Plotted over time, we can start to look at trends of how battery capacity is changing. In the most recent study, we looked at over 5,000 vehicles, and many trips.” Geotab saw that the average degradation rate was just 1.8 percent per year. In Geotab's 2019 study, it was 2.3 percent per year. “This most recent study didn't have as many of the early-gen vehicles,” says Argue, “telling us that battery management systems are getting better, and batteries are lasting longer.”

If this 1.8 percent annual degradation continued in a linear fashion, after 10 years an EV would still have 82 percent of its battery capacity, much more than the 70 percent most batteries are warrantied for after eight years.

Dial that forward 20 years and the car would still have 64 percent. If a vehicle started off with 300 miles of WLTP-rated range (the standard test cycle used in Europe), it could have 192 miles of range 20 years later. That remains quite usable, and now there are lots of cars on the market that begin with well over 300 miles of WLTP range.

We Don’t Know How Long EV Batteries Will Last … Yet

Of course, there is still guesswork involved here, because there are no 20-year-old mainstream EVs, and precious few even over 10 years. Many of the latter are Nissan Leafs, which lacked the thermal management that keeps batteries in their best health, so they probably aren’t the best guide for more modern EVs.

But BMW i3 cars from a decade ago are reportedly faring well, with most still providing over 80 percent of their original capacity. BMW, which has conducted its own studies, confirmed to WIRED that i3 batteries have lasted considerably longer than the company expected. Indeed, in 2023, BMW UK purchased the oldest i3 the company could find in its Approved Used network for testing. It was a 2013 BEV model fitted with a 22.6-kWh battery, chosen purely on age. The car had 83 percent battery capacity after almost 10 years on the road.

Tesla Model S vehicles from 2013 show a similar capacity, according to Plug In America results reported by Nimblefins. Tesla even has a 2015 Model S in its UK press fleet with more than 250,000 miles on the clock, on the same battery, with approximately 86 percent of its original capacity remaining.

However, Argue advises caution. “We can't predict the future. It's 1.8 percent per year to date,” she says. “There is an argument that there could be what we call a heel curve towards the end of the life of the vehicle, where the battery starts degrading faster than it did for most of its life. We haven't observed enough bad vehicles hitting that heel to be able to predict or analyze when that will happen. All we can say right now is if it continues to degrade at the average rate that we're seeing, these batteries should last 20 years or more.”

“We do see variation across different vehicles and models,” continues Argue. There are other factors as well. “So far, we haven’t seen a significant impact from high mileage on degradation rates, so you shouldn't be afraid to use your EV.” This finding is in line with P3’s research.

“But we have seen a correlation with the frequency of DC rapid charging,” warns Argue. “Cars that frequently rapid-charged did have an observable increase in degradation rates.”

Hot weather is also a factor that affects durability. “The worst case was three times more for a particular model driven in hot climates and using frequent rapid charging,” says Argue. This would mean losing 5.4 percent of battery capacity per year. However, “the best had on average 1 percent degradation per year. It's definitely a positive trend we're seeing.”

“When the electric vehicle market started, there was a large concern around the factors that can lead to increased battery degradation,” says Neil Cawse, CEO of Geotab. “For example, discharging completely, charging in cold weather versus warm weather, using high-speed charging versus low-speed charging. But battery tech has gotten much better, particularly around management systems—for example, making sure that lithium-ion cells charge properly when cold.”

This better battery performance could provide longer warranties for a higher remaining capacity. Toyota already offers a 10-year warranty on its EV batteries, and MG has been experimenting with a lifetime guarantee in Thailand. “You still generally have warranties that promise 70 percent state of health at eight years, but the degradation that we're seeing on those batteries is much less,” says Wallace.

Your EV Could Still Be Good After 20 Years

However, research so far has been based on how the car’s systems report the battery’s state of health. “I would take all those values with a pinch of salt,” says Wallace. “The reported state of health on the dashboard that the customer sees is often significantly different from what the actual state of health is from that battery.” According to a report published by Elysia in 2023, the true state of health can be up to 9 percent different from what is reported.

Another issue is the buffer that manufacturers leave in their batteries, which is the difference between the net and gross capacity in kWh. “OEMs are oversizing these batteries,” says Wallace. However, Argue explains that “there must be some safety buffer, because what we know from battery science is that if a battery sits completely full or completely empty for a prolonged period, that causes more stress. Having a buffer protects the battery from degradation.”

Wallace reckons this buffer is overly conservative, given the low degradation being seen with EV batteries. “They don't need as much excess capacity,” he says. “Smaller buffers mean smaller batteries, bringing down the cost of EVs.” Trouble is, Wallace believes many traditional automakers don’t yet have the necessary data about their own batteries to take this step.

Still, if batteries continue to last like the studies from P3 and Geotab imply, EVs could well be in better condition than combustion engine vehicles of the same mileage and age. The rest of an EV is less expensive to run as well. “The cost of maintenance is significantly lower,” says Cawse. “You maintain the brake pads and change the wipers—and that’s about it.”

A 10-year-old EV could be almost as good as new, and a 20-year-old one still very usable. That could be yet another disruption to an automotive industry that relies on cars mostly heading to the junkyard after 15 years.