I am new to the RVing too, and just bought an RV from my friend who was original owner. He is a retired highly decorated auto-mechanical engineer. In any case, he just told me today that he had REPLACED original 4x6V battery system which he PURCHASED as an option(!), with 2x12V system, which is what it has now, and advised me to check those batteries, as he knows they had recently were left to die due to fires.
So now, I am reading here, that 6V is considered better than 12V.
He said that he did it after original 6V batteries finally gave up, and he found himself in a situation were 6V batteries were not available or be prohibitively expensive, so he downgraded to 2x12s as, he said, they are offering similar performance, but give much more flexibility, easier to source, and cheaper than 6Vs...