The Sinclair C5 battery charger and battery was ahead of its time. I remember my Dad (who was something of a lead acid battery nerd) being very excited about it.

The battery in the C5 was designed to be run to 0% charge which would kill most lead acid batteries in no time, but if I remember rightly the charger would recover them by putting quite high voltages across them to de-sulphate them. Or something like that (not a lead acid battery nerd :-).