I went back to a Tacoma from a FJ, before selling it I removed parts I would reuse in the tacoma one was the dual battery system and the marine Optima battery. Before getting the Tacoma I assumed the Optima would just drop in to the passenger side wheel well like on the FJ. I've seen other dual battery set ups with both batteries in the OEM spot, I didn't want all that weight in one spot
The '13 has some stuff in the way that made the install a little harder.
There is some DENSO electrical box and a air pump for the emissions in the way that needed to be relocated (anyone know what it is?)
After moving them out of the way I needed to cut 3 bolts that were in a tri-pod shape on the inner fender, maybe a mount for a non-USA Tacoma jack? Then I was able to sit the battery box in place to figure which direction to mount it.
I was able to drill three holes to mount the battery box, the one closest to the fire wall needed spacers to hold it up level, (you can see the white plastic spacers underneath)
I got the air pump bolted back in but it was moved over about 1 inch and was only able to reuse 2 of 3 bolts.
Next I ran the wires for the dual battery kit http://www.dfna.info/dual-battery-kit.html# a very simple install.
And made a mounting bracket for the isolator, in the FJ I mounted it on top of the fuse box but it was a PIA to open fuse box. I bought a small plastic cutting board and cut it to size and a piece of angle iron.
I ran the wire from the main battery to the isolator, another wire from there to the hot side on the aux battery and ground isolator + aux battery.