your battery is most likley killed, check all your grounds and battery ends if they are good and tight, then have the battery load tested. Most chargers just charge and top off and stop charging by voltage capacity rating(ussually 12.2-12.8 volts) and not cca amp capatity. Most batterys can get back to the 12 volt range showing good but, putting it under load in that state instantly will drop voltage like a rock. this is ussally what will kill the alt fast also. Its under constant load trying to charge what I call a black hole. Hope this helps.