Battery maintance get your hands on an old ac adapter from battery drill, cacl. ect be sure the output is 12v dc limit the amps to 25 ma. phone company used 1000s, of these on phones. put a aligator clip on the ends black for - neg. red for +pos. put in on battery for a few days each mo check voltage after you disconnect it but wait about an hour first.
It should keep it just right