After 36 months and 45K miles, no change
Last November, I turned in my 2013 Smart EV lease after 36 months and almost exactly 45,000 miles. There was no detectable change in it's range- I would still get "about" 7 miles for every 10% of battery, depending on conditions.
At that time, I wanted to buy it from Mercedes, but they insisted that I pay something like $13,000 for it (not counting the battery), because that is what the "Residual" was at the end of the lease (which allowed for the very small lease payments). I was extremely disappointed, turned that great little super reliable fun to drive car (with integral seat heaters) and bought a 2015 orphan EV off of them they were anxious to sell. It had only 30 miles on it, and doing so allowed me to take the 3K tax deduction- but it does not have built in seat heaters :-(
A year later, it has experienced more issues than the 2013- most recently "Bucking" and eventual total Shutdown- which was eventually traced to a wire bundle in the vicinity of one of the rear wheels in which there had been some chafing that was periodically shorting the CAN bus.