dual battery set-up

[02LaunchSS]

adding another amp and two more tower speakers, so I want to go to a 2 battery set-up. any ideas on where to get a wiring diagram (of the way supra wires this up one the new ones) and the parts (correct gauge wire, battery selector switch, etc.) Thanks!!!

[propwash03]

I have a two battery setup on my boat and it works great, I would recommend getting a wiring diagram for my boat ('04 SSV GG) and wire them up that way. My stereo only pulls from one battery, and both charge while engine is running. I can completely drain the stereo an accessory battery (same battery) and I can still start the boat off of the other one. There are no manual battery switches involved, don't know how they're wired, but they work great!