problems with my 240sx se w/hicas battery keeps dying

[cb40]

i checked the battery with a tester and it reads a full 12 volts we put it in and tried to start the car and nothing. we tried to jump start it and after a couple minutes it started. we also tried charging the battery with a battery charger and the unit read that the battery was fully charged? how would we check for a draw and where should we start? Thanks alot for your help!!

[Mez_DK]

alternator?

have it checked.