Most manufacturers offer extensive battery warranties, for example Nissan offers an 8-year, 100,000-mile battery warranty on the new LEAF. Nissan has in fact recently stated that the battery pack of a Leaf will last for approximately 22 years; 10-12 years longer than the average life of the car itself. This is based on recent battery degradation data from 400,000 Nissan Leafs sold across Europe.
There are first generation Nissan Leafs still in use which have driven over 150,000 miles. A well looked after vehicle, which has driven in excess of 100,000 miles, will normally have only lost up to 10% of its battery capacity. This figure is likely to improve as battery pack innovations are introduced into the next generation of EVs.