AS EVERY MOBILE-PHONE owner knows, after a year or so the battery starts to fade and the beast needs recharging more frequently. That is a nuisance, but a phone’s batteries can be replaced fairly cheaply—or the whole handset traded in for the latest model. An electric car, however, is a much bigger investment. And batteries are its priciest component, representing around 30% of an average mid-size vehicle. Apart from increasing the risk of running out of juice and leaving a driver stranded, a deteriorating battery quickly destroys a car’s second-hand value.
To provide buyers with some peace of mind, carmakers guarantee their batteries, typically for eight years or around 200,000km. Producers are now, though, planning to go much further than that, with the launch