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If the 24's are 75 AH rated and the 6 volts 225 AH rated I would expect the 6v option would out perform because a lot of physical/electrical issues getting three batteries that will not fight when laced together in such a manner to yield 12v output. Other wise 225=225 AH on paper.
You may want to look at your full needs in light of AH and the cost per AH. We found more ban for the buck with our old MH to spend the money on tires, roof, cooling system to make it road worthy to the max. Solar is nice but so are a lot of other things. Keep up with hours you run your generator currently and associated costs and AH consumer is one approach.
