I checked the archives on this subject but I am not quite sure that I got all the subtleties so I am posting this rather long winded question.I was helping a friend with a new to him Endeavor 32' and one of the tasks I did was to replace the two 6V golf cart batteries. I got GC 15s to replace the old GC 2s (that is what they had on hand, saying only that the GC 15 has more plates which sounded good to me except the $120 price per battery). The battery store guy also said the old GC 2s looked like they had been overcharged or perhaps were frozen at one point as the cases were bulging a bit. The GC 2s were only from 2005 according to their dating label and would only show about 10V (at best) on the on board battery tester/meter and we had some trouble starting the engine off the ALL battery switch which included a new deep cycle marine 12V battery. The alternator was also shot which was contributing to the problem and was taken off and rebuilt and re-installed by me.My questions are these: Could the charge produced by the newly re-built alternator possibly overcharge the GC 2 or 15 batteries? Some of the info I found in the archives indicated that certain batteries do not like to be recharged with a voltage higher than 14.1 volts (would this apply to GC 2 or 15s?) whereas deep cycle batteries like to get the higher 14.4V charge? Could the alternator be giving too much charge for golf cart batteries? If so is there any way I can introduce some resistance to the charging circuit for the GC 15 bank to bring the voltage down to something more like what they would prefer? The alternator produces around 50 amps which is roughly 1/4 the amp hour total of the entire bank which is in the ball park for reasonability,Any help from anyone who has been down this road before will be greatly appreciated.In over my head but still learning and swimming.