A British company is launching a smartphone app that can calculate the state of health of an electric car's drive battery.

Costing around £30 and due to be launched in the coming weeks, Clearwatt’s EV Health Checker uses an EV’s connected car data and information from the driver’s smartphone to provide a detailed picture of its real-world efficiency and performance.

The resulting report gives a grading for the EV’s battery health relative to a new vehicle and comparable vehicles; an estimate of its future battery degradation based on past performance; and a prediction of the car’s range in a variety of scenarios.

It also shows the impact on the car’s range of the wheels fitted to the vehicle.

Historically, EV battery data has been difficult to obtain and, even if you have been able to acquire it, the information captured and its presentation differs between manufacturers.

This has made it almost impossible to provide a standardised representation of an EV’s battery health for used car buyers.

During last year’s general election campaign, the Labour Party – with an eye on the used EV market – promised to introduce a battery health standard to make information clearer and more understandable, but this has yet to materialise.

Geotab, a leading telematics company, recently reported that while the latest EV batteries are degrading at an average rate of 1.8% per year, compared with 2.3% in 2019, they continue to be sensitive to factors including ambient temperature, thermal management and charging patterns.

In particular, batteries are affected by how frequently they are rapid-charged. Geotab found that rapid-charging a battery more than three times per month can accelerate degradation by up to three times the average rate.

This risks undermining the appeal of that future staple of the used market: the three- to four-year-old, 60,000-mile, ex-company EV that has been frequently driven on motorways and subjected to regular rapid charges.

Patrick Cresswell, cofounder and managing director of Clearwatt, believes that this is a legitimate concern.

“Currently, most EV drivers don’t own their car and so aren’t on the hook for its condition,” he said. “For example, a sales rep is likely to rapid-charge their car as often as they require and even override the automatic 80% charge limit, all without liability. This will accelerate battery degradation.

“We monitor a lot of EVs with annual degradation rates well in excess of 1.8%.”

The British Vehicle Rental and Leasing Association publishes a fair wear and tear guide describing the condition that its members expect cars to be in when they are returned. A spokesperson said that because there’s no agreed battery health standard, it hadn’t been possible to include battery health in the guide but that this was under review.

British Car Auctions (BCA), a major source of ex-fleet cars, recently launched a grading system that it claims offers a “perfect at-a-glance” view of an EV’s battery.

The BCA Battery Health Grading system is conducted by connecting a diagnostic device to the EV’s on-board diagnostics interface. The resulting report reveals the battery’s remaining capacity, scoring it out of 100, and highlights any “red flags” related to defective battery modules.

However, Estelle Miller, co-founder of EV Experts, a specialist dealership in Surrey, believes that it and other test tools and report styles risk confusing buyers.

She said: “The available driving range displayed on the car’s dashboard is fine, but you really need to know the battery’s state of health. We use a diagnostic tool that expresses this clearly as a percentage.

“However, we recently saw a report on a used Volkswagen e-Up that had what the company that tested it called a ‘high health score’ when it actually had a very low battery state of health – a figure that was sneaked in at the foot of the report.

“My fear is that some test methodologies are overcomplicating things to mask higher levels of battery degradation.”