I have received 2 of the 3 amps that I'm putting in my new system and think that I may need some additional battery time. they are 3 rockford fosgate punch series amps and all 3 call for 100amp fuses, which tells me that they will draw a lot of current, not that we'll need it for parking, but never be too sure.
I already have a 2-battery setup with the switch and have 2 new interstate 800cca deep cycles. one is wired just to the engine and the other is wired to the 2 kenwood amps and then to the fuseblock under the dash.

I am assuming(yea, I know) that I can add a 3rd battery and just wire it with the battery that powers the stereo/fusepanel in parallel? run the positive leads together and the neg. leads together?

the setup now is as follows:
power from main engine area runs to the center post of the switch. one lead to each battery from there.
ground from main engine area runs to the engine battery first, then there's a short lead from the engine's battery to the acc. battery.

thoughs?