Nice writeup on re-using a car battery for solar power storage. Most car batteries still have a little life left too them (just 1/2 cells are dead) so if you need a cheap storage for solar, this is a good way to go about it. It may not be the best way….
http://www.instructables.com/id/Uses-For-Dead-Car-Batteries-And-Sealed-Lead-Acid-B/