Used EV buyers are checking battery health, and the numbers are not as bad as feared

When Kerry Dunstan and his partner bought a 2021 Nissan Leaf this summer, the first question they asked the dealer was about the battery. The answer, around 93% state of health, helped close the £12,500 sale. The BBC reported the couple's experience on 16 October.

State of health (SOH) is the percentage of original capacity a pack still holds. It has become the number used EV buyers want before they sign, in the same way mileage and service history once dominated the conversation. Austria-based Aviloo issues battery certificates for UK auction house British Car Auctions. It offers two tests. A premium version logs a few days of driving from 100% charge down to 10%. A flash test, Aviloo says, can be completed at a standstill in under two minutes. Chief product officer Patrick Schabus told the BBC the company can "completely independently, determine the state of health of a battery".

A replacement pack is expensive, so the stakes are high.

NPR reported on 2 March that a new high-voltage battery can cost in the ballpark of $5,000 to $20,000. In 2010, the New York Times wrote that estimates of EV battery pack lifespan ranged upward from seven years, NPR noted. The average car on the road is more than 12 years old. That gap made buyers nervous.

Pooled data now points the other way. Cox Automotive, which runs used car auctions, has tested nearly 80,000 EVs and found an average battery health of 92%. Its vehicle services director, Adam George, told NPR the company had expected "mass degradation over the first one to three years". Instead it found two to four-year-old off-lease cars returning with scores well above 95%. Recurrent, a research firm drawing on more than 30,000 drivers, describes ageing as an S curve: a quick early dip, a long plateau, then a faster decline at the end. Its director of market insights, Liz Najman, compared it to breaking in a pair of shoes.

Recurrent's community data also covers older cars. Among EVs ten years or older, only 8.5% have ever had a battery replacement, and more than 90% still run on their original pack. For EVs of any age past 150,000 miles, Najman said owners are getting at least 83% of original range. "EV batteries are holding up phenomenally well," she told NPR. Warranties typically cover at least eight years and 100,000 miles, and defects are usually handled under them.

Chemistry has moved too. Max Reid, head of battery costs at market research firm CRU, told the BBC that older batteries might last 500 to 1,000 charging cycles, while some new EV cells now reach 10,000 cycles. Even a pack below 80% SOH can still be useful, according to Aviloo chief executive Marcus Berger, who said such a car "just needs to be priced appropriately".

Two problems remain. Aviloo's Berger said his firm's results sometimes diverge substantially from the SOH figures produced by cars' own built-in systems. Paul Chaundy of Second Life EV Batteries in Dorset told the BBC: "We need more standards around that, I think." Charging advice is still unsettled. Simona Onori at Stanford University said there is likely a sweet spot between frequent fast charging and avoiding it altogether, but added that to her knowledge it has not been thoroughly studied.