What size of battery? AAAA, little 9V or car battery?
What voltage? 7.2V for radio controlled toys?
What chemistry? Lead-acid, Ni-Cad. Ni-MH or Lithium?
How quickly do you want a full charge to complete?
Do you need a discharge cycle before charging?
Do you want it to be automatic and go to a trickle charge when fully charged?