When Kerry Dunstan and his partner looked for a new electric car this summer, they asked one key question: “How’s the battery?” They found a 2021 Nissan Leaf with 29,000 miles on the clock. The dealer told them its battery’s state of health (SOH) stood at around 93%. That figure convinced them. For £12,500, they got an electric car with plenty of space and a roomy boot.
Kerry Dunstan, a cabinetmaker who also owns a stylish electric Volvo SUV, hasn’t quite bonded with the Leaf. “I like sporty, jazzy cars – and it’s just a bit ‘meh’,” he says. Still, he admits the Leaf has performed exactly as expected in the three months since they bought it.
A new focus for used car buyers
Buyers once checked only age and mileage when shopping for second-hand cars. Now, as electric cars rise in popularity, battery condition has become the real headline figure. Buyers want to know how the battery was treated. Did the previous owner often charge it to 100% using a fast charger? That habit can shorten a battery’s life.
This uncertainty has made some drivers hesitant about buying used electric cars. But new battery analytics firms claim they can assess battery health with high precision. Experts even say many electric cars last longer than early forecasts suggested.
Take Dunstan’s Nissan Leaf, for example. It lacks the advanced liquid cooling system common in other electric models. Nissan corrected this in newer Leafs, but older ones show a clear range loss over time, according to data from US research firm NimbleFins. Dunstan remains calm. “I charge both my EVs to 100% when needed. I don’t worry about it,” he says.
Technology reveals battery secrets
For worried buyers, Austria-based Aviloo promises answers. “We can independently determine a battery’s state of health,” says Patrick Schabus, the firm’s chief product officer. Aviloo is one of several battery analytics companies working in this field. It provides battery health certificates for major UK auction outlet British Car Auctions and offers two main tests.
The premium test requires a data logger the size of a glasses case. Drivers plug it into their cars for several days, letting it track the battery’s performance from full charge down to 10%. The second option, the flash test, is faster. It collects battery data through the car’s management software and analyses it with a computer model. “We can do this in under two minutes,” says Schabus.
Aviloo says its detailed test tracks fluctuations in current and voltage and reveals the condition of individual battery cells. Chief executive Marcus Berger adds that his company’s results sometimes differ sharply from cars’ built-in battery readings. He also challenges the belief that batteries below 80% SOH are finished. “An EV with 75% SOH can still be a great car if priced correctly,” he says.
Real stories from the road
In New Zealand, EV owner Lucy Hawcroft remembers her own experience. She and her husband bought a Nissan Leaf three years ago. The dealer told them its battery was about 95% healthy. But a year later, an independent check showed a noticeable drop. “My husband was surprised, maybe a bit concerned,” she recalls.
Still, the Leaf runs around 160km on a full charge. They mostly use it for short trips under 10km. Hawcroft admits she envies friends whose EVs can go 400km. “That would be ideal,” she says.
At Cleevely Electric Vehicles in Cheltenham, detailed battery checks play a major role in sales. “Most customers want this information,” says David Smith, the firm’s sales director. His company uses independent SOH reports from ClearWatt. “We can’t alter the reports,” he says. “Seeing them helps sell the car in nine out of ten cases.” Managing director Matt Cleevely adds that replacing small battery modules often costs far less than installing a whole new battery.
How to charge smartly
So how should drivers charge their cars to keep batteries healthy? Simona Onori from Stanford University suggests moderation. “There’s likely a sweet spot between frequent fast charging and avoiding it completely,” she says. Research still needs to confirm that.
Battery technology itself keeps improving fast. Max Reid, head of battery costs at research firm CRU, explains that older EV batteries lasted 500 to 1,000 charge cycles. “Now some new cells reach up to 10,000 cycles,” he says.
And when a battery no longer suits a car, it can still serve other purposes. Paul Chaundy from Second Life EV Batteries in Dorset says many businesses reuse old EV batteries for storage. Some companies power forklifts with them when their grid connection limits how many charging ports they can run.
As for differing manufacturer methods of calculating SOH, Chaundy calls for clearer rules. “We need more standards around that,” he says.
