2000 Chrysler Concorde batteries goe dead. won't start

originally put in new battery, found out the cable battery to stater from battery was really corroded, fixed that problem lasted about 2/3 weeks now have same problem. tested the alternator, it was good. My son has chrged this new battery 2/3 times now and still no start. Im guessing something in the secruity system, is there a fuse etc to check for this, or can he somehow disconnect the system to by pass the shorting of the battery.