Well, when they're not strong enough for riding anymore, please dispose of them properly. Or, even better, they can usually store some charge for quite a long time, so some people have managed to hook them up to their solar/house battery array along w/ old car and laptop batteries.
I cant get down with the folding bikes...the small tires give less control...more mechanically complicated...for what?...so it takes up a square area instead of a rectangle?