I'll go against the grain here. IMO, unless you are running an amplified stereo for hours on end, I would just use 2 of the pack batteries.
My 1998 cart has used 2 of the batteries in the pack for a 12v connection since it was new. I have headlights, tail lights, horn, signals, cigar lighter and 12v accessory plug. My batteries were 2004's until a few weeks ago when I upgraded to a 48v system and changed the 6v batteries to 8v. The batteries were all even, came up to 6.4v each, load tested fine and would easily do 36 holes plus additional driving. I expect they would have gone at least a couple of more years.