I did what Old Biscuit suggested in his last line - I have 2 each 12-volt Grp 29 batteries in parallel.
I am a big fan of 6-volt batteries - had 4 of them in my trawler (replaced a stupidly heavy 4D), but in an RV where you have 2 each 6-volts in series you are completely dead if one of the 6-volts dies. If one of my Grp 29 batteries dies, I still have the other one working until I can get the dead one replaced.
I'm no expert but none of the 4D batteries I see are deep cycle. I understand they were originally developed as tractor/dozer starting batteries. Someone feel free to correct me if that is wrong.
