Steve., when you put two batteries in parallel the best way is like this.
(Ignore periods in the next two lines
Ground|-{Battery1}+
. . . |-{Battery2}+==Fuse and distribution panel and charger
This way you do not worry so much about resistance as it's the best balance you can get. You may reverse 1 and 2 since those are arbitrary by the way.
As someone said: With 2 in parallel there is a CHANCE one may short and take out the other leaving you with nothing.. There are a couple other failure modes. and when I had one short it did not take out the others. as once I removed the shorted cell they all pass tests (load and duration of run on inverter power for house)
So the key word in that phrase is CHANCE.. There is a CHANCE (A good one) that won't happen.
The reason I like a six volt pair is simply cost. Best bang for your buck.
