“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.
