There are two or 3 things that give the edge to the 6 Volt GC-2 class
1: as noted they are easier to install and remove.. This is major. a 12 volt battery of the same amp hour is 2x as heavy and my Deka GC-20's (230 amp hour GC-2 class) I can not install by myself. I could hte older U-2200's (interstate) but they are slightly smaller. that is my "Limit".
2: The "Golf Car" battery is a TRUE DEEP CYCLE. Most folks when they talk abou 12 volt batteries are not discussing the 8D or 4D they are talking about "Group-XX batteries (24/27/29/31) and though you can get 'em in Deep Cycle. most are MARINE/deep cycle. which is not a deep cycle battery.
And finally
COST.. The GC-2 is the most popular battery of it's type so line re-tooling does not happen as often... if ever.. and that reduces the unit cost of the battery.
BUT: Technically 230 amp hours of DEEP CYCLE battery is 230 amp hours of DEEP CYCLE battery. it does not matter how you get there.
HOWEVER 230 amp hours of DEEP CYCLE battery is better for house battery use than 230 AMP HOURS of MARINE/deep cycle battery.. by about 2x.
