Thought I would share some pics of my add a battery install - it's a work in progress. I cut a hole behind the battery switch and ran the battery cables thru it for easier cable routing and a cleaner look (both batteries will go behind the panel that the battery switch and ACR are mounted on). I am using thermal circuit breakers all around instead of fuses (thanks for that tip Razz!). One thing I learned is that you can use 2/0 welding cable instead of 2/0 battery cable. It's a lot more flexible (uses much finer strands compared to battery cable) and easier to work with and is about the same price. I only needed a couple of feet to go from the battery to the battery switch.

BTW, all of the speaker wires hanging on the left is the stock wiring that I am replacing. Have not gotten around to cutting them yet.