Asking here shows an intention to learn, I guess.
So, for those who are trying to learn, a translation: 3-cell battery = 6 volt battery.
My take on it is that the "buzz" is largely caused by lower cost of a pair of 6V, compared to same 220 AH capacity pair of 12V. Crowds that killed their single 80 AH battery happily provided by the dealer with new RV, are looking to replace and discover 2*6V :)... They buy a pair of cheapest no-name 6V and live happily, - or not so happily.
I don't think that I will replace my 3*12V AGM bank with 2*6V any time soon, since it works for me, while 2*6V flooded will not.