The Renault idea is terrible. Why should you lease something that should be included in a steep purchase price?
The reason mobile/laptop batteries don't last long is due to who they're manufactured by, how advanced they are and people not following instructions on longevity. My Insight's batteries were manufactured by Panasonic and likewise had a warranty of 8 years/100k miles - bear in mind this is a warranty that is comparable to a rustproofing warranty on a new car! Manufacturers won't give you anything near that on anything even remotely wear and tear. A modern diesel will need the DMF replacing at least once in the same time, as way of comparison. My Insight's were still holding perfect charge after 11 years and that is late '90s technology.
The Leaf, and I assume the Tesla, will ask you to plug it into the mains every night to condition the battery and keep it tip-top much like a trickle charger.
