How to tell the health of a battery in a used EV

When Kerry Dunstan and his partner looked to buy a new electric car this summer, one of the questions they asked was: “How's the battery?”

They found a 2021 Nissan Leaf with just 29,000 miles on it and the dealer told them the battery health, or battery health (SOH), was still around 93%.

The pair were sold. For £12,500 they got an electric car with a big boot and plenty of space for passengers.

Although Mr Dunstan, a cabinet maker who also owns a slightly posher electric Volvo SUV, isn't entirely in love with the aging Leaf.

“I like sports cars, jazzy cars – and this is a little meh,” he says.

However, he adds that the Leaf performed exactly as expected during the three months I owned it.

Age and mileage used to be the top two headline details that potential used car buyers pondered. But as more people go electric, checking the health of your car battery may become even more important.

How was this battery treated? Did the previous owner regularly charge it to 100%, for example? What has the opportunity to reduce Electric vehicle battery life.

This problem is with the battery black box supplied some consumers from buying a used electric car. But battery analytics companies say they can accurately determine the health of an older EV's battery. And industry experts say some electric vehicles are lasting longer than many predicted.

Take Mr. Dunstan's Nissan Leaf. This model of electric vehicle does not have the complex liquid battery cooling system found in many other electric vehicles. While Nissan fixed this in the last generation Leafs, earlier models show a significant reduction in their range every year, according to analyzed by US insurance and research firm NimbleFins.

Mr. Dunstan is unperturbed. “I charge both my electric cars to 100% and put them on charge when I need to charge them—I don't worry about it,” he says.

However, for people looking to buy a used electric car and suffering from battery anxiety, Austrian firm Aviloo says it has a solution. “We can actually determine the health of the battery completely independently,” says Product Director Patrick Schabus.

Aviloo is one of several battery analytics companies on the market. The company, which provides battery condition certificates for British Car Auctions, a major British car dealership, offers two products.

There is a premium test in which electric vehicle owners attach a data logging unit, about the size of a glasses case, to their car so it can track battery performance as they use the car over the course of several days, going from 100% charge to 10%.

Or they can choose a faster flash test, which uses a different unit to collect data from the car's battery management software and then analyze it using a computer model. “We can do this non-stop in less than two minutes,” says Mr. Schabus.

The premium test closely monitors battery drain, capturing fluctuations in current or voltage, and can provide additional detailed information about the health of individual battery cells, Aviloo said.

Markus Berger, chief executive of Aviloo, says his company's analytics results sometimes diverge “significantly” from battery SOH percentages reported by some vehicles' built-in analytics systems.

He challenges conventional wisdom that batteries with SOH below 80% have gone too far: “An EV with SOH below 80% can still be a great car… You just have to consider the price.” [appropriately]”

In New Zealand, electric car owner Lucy Hawcroft, who works in sustainability for an infrastructure firm, bought a Nissan Leaf with her husband about three years ago. She recalls getting an SOH score of about 95% from the dealership. But a year later, an independent mechanic checked the SOH for them again.

“He fell a little bit,” she recalls. “My husband was a little surprised or concerned about it.”

However, when fully charged, the car still has a range of around 160 km (100 miles). The couple mainly uses it for short trips of up to 10 km. Ms Hawcroft says she has friends whose electric cars have a much longer range, around 400km: “That would be ideal.”

For David Smith, sales director at Cleevely Electric Vehicles in Cheltenham, the ability to analyze used EV batteries in detail is crucial. Most clients ask for this information, he said. His company uses SOH reports from ClearWatt, another battery analytics company.

“They are completely independent. We can’t interfere with reports,” he says. “Once customers see the report, it will help sales nine times out of 10.”

Matt Cleevely, managing director of Cleevely Electric Vehicles, adds that it is often possible to replace groups of cells or modules within a battery – much cheaper than installing a completely new battery.

As for how you should charge your own EV to better care for its battery, Stanford University's Simone Onori says, “There's probably a happy medium between frequent fast charging and no charging at all.” However, she adds that, to her knowledge, this has not yet been thoroughly studied.

Despite some consumers' wariness, battery technology has improved markedly in recent years, says Max Read, head of battery costs at research firm CRU. “Old batteries can last from 500 to 1000 [charging] cycles,” he explains. “Now some of these new EM cells are going through 10,000 cycles.”

“Batteries that are no longer suitable for the electric vehicles they were designed for can still be useful,” says Paul Chaundy of Dorset-based Second Life EV Batteries. For example, some of his clients are businesses that use former electric vehicle batteries to store electricity on their premises. They might have, say, six electric forklifts, but the network connection is large enough that the charging ports can power two or three forklifts.

Regarding the different methodologies that car manufacturers use to create SOH reports for their vehicles, Mr. Chaundy says, “I think we need more standards in this regard.”