Question about battery "ampacity", wiring, etc

[jbeez 0]

Say I have a group of rear batteries near my amps, but I also of course tie in with the front of the car. At the front of the car is a factory 175A alternator, and a stock group 65 battery. How do I figure how much current I could draw from that area so I can run the appropriate wiring. Also I'll be replacing the front battery with an xspower D6500, I want to run the wire that will support that and the alternator instead of doing that later, so I guess maybe the factory battery doesn't really matter in this, but I'd still like to figure out if what I have now is even a bottleneck currently. Waiting for some new amps to arrive and while that goes on I'm doing everything I can to cleanup all of my electrical and make sure its ready to go when the time comes.

Thanks,

-Jerry

[jbeez 0]

Sorry for posting extra, I cant seem to edit my last post though,

Assume 3000w for a 6500D, so if i calculate at a bad voltage of maybe 12v that seems that supporting 3000W @12v will require about 250A of capacity in wiring. Is that the proper way to go about that figuring?