Hello, I am new to the forum. We have a 30' 5th-wheel with an onboard, 4kw, Onan, 12v. start, propane generator. Our current batteries are 2 12v. Grp.24 DC (from Walmart) in parallel. The are getting tired and will need to be replaced soon. Our existing batteries can discharge on a cold night, (furnace fan is on a lot) such that the generator will not start. I have to go outside, plug in the truck, start the truck engine and wait until I can start the generator to charge the house batteries. I think that I can fit two Costco 6v golf cart batteries in the battery trays and hook them up in series. I know that I can fit two grp. 27dc marine batteries in the battery trays and this should provide additional reserve power (a little more than the grp. 24's), and is a good starting battery. The question is: although the 6v. gc batteries should give me a lot more reserve power for the 12 v. house requirements, will they crank over the generator? The weight per battery is similar for both types.