Switched to 6 volt batteries

'Usable' amp hrs is greater with a 6v than 12v...

That is why I use the expression 3-cell 6-cell and 2-cell.

The GC-2 is a bit taller, but a lot more capacity, Plus it's a TRUE deep cycle, which is why I highly recommend them.. But you figured that out.

OH, and it's still a 12 volt battery.. Just two pieces for easy handling :)

Yes, 2 typical 6v will give you more AH capacity per footprint than 12v.
But for the given physical size and weight, there is no difference worth haggling over.
For example, 2 6v colf car batteries have basically the same physical size and weight as 2 group 27 12v batteries, and they have basically the same AH capacity.
So,......what was the question again ? :)

Great install and video clip - sound explanation as well!!