Last one to post in this thread wins!

Ok I checked Napa website and they have the #4 6 volt battery that is factory x`s 2 of what is in my small diesel. They are at 118 each. Would you guys go with a single 12 volt or replace both 6 volts like it is now?
I think the 6 volt would have a larger amp capacity than a 12 volt but not sure just a guess.