As an owner of a 2014 Mercedes B-Class Electric and now a 2013 smart 451, I can tell you that both have about 80% or more of their original capacity and are going fine. Like the smart, a few B-Class electrics have catastrophic (motor/controller) failure that ends the car's life prematurely. But aside from those special cases, like "MB DNA" says, nobody knows the life expectancy. On cargurus.com you can find 2012 Tesla Model S's selling for over $30k. So far so good!