What might cause bulges in Trojan flooded batterie

Having been involved with battery chargers for electric golf carts I have seen this happen numerous times.  Trojans are the gold standard for golf cart batteries.  If batteries get overcharged, due to charger malfunction, the electrolyte can boil and boil for extended periods of time, resulting in bulging of the sidewall.  The only other times I see this is if the battery is way undercharged and is then subject to freezing or below temps, resulting in the same. Was there ever a period of time where you were without power and the charger would not have been charging?  Check the following: when on the Dewalt charger are you reading 13.5 or 13.6 v on your multimeter?  Disconnect charger and let your batteries rest for 4 hours and read voltage, then do the same 24 hours later making sure there are no phantom draws on either battery, the readings for both times should result in no more than 0.02v difference if the batteries are good. 

Last year I trickle charged my Trojan T-1275 battery for 24 hours at 2 amps, first week in November.  After that I disconnected from charger and set both batteries (the other is a 12v Interstate deep cycle) directly on the concrete floor in an unheated garage, making once/month readings to make sure they were holding charge.  The last reading was taken May 1 the following year (6 months after the November charge) and the voltage was 12.54, not too bad after 6 months.  The other battery was only 12.38v but considering it is 12 years old, I am not complaining.