Don, when I had the solar install done, AMSolar put 4 4GT-6CTs in after first considering the 4CT. They are 6 volt, 2 pairs seriesed, then both pairs paralleled. At 300ah each, but having 2 pairs seriesed, gives 600ah total available, then should only use down to 50%SOC to prolong life. Just discussed LiPO4 units this am at their shop--came to conclusion would lose to much on the good batteries just to swap out. But will go Lithium if my ship ever comes in...
They are GOOD batteries.
2016 Tiffin 40QBH
2005 36TK3--retired, but it was a good one
2017 F450 KR