Most EV manufacturers provide a warranty of eight years or 100,000 miles (whichever comes sooner) for the batteries. 15k a year is a lot for an electric car, but the batteries will still be under warranty for more than 6.5 years. After that, they're unlikely to suddenly fail - rather, they'll slowly degrade over time. Around 8-10 years is probably a fair expectation - by which time, you'll have saved a lot of money in servicing and maintenance (not to mention fuel costs) compared to a petrol or diesel car covering 15k a year.