@3.6, if i have both batteries under the hood i only have to run one wire back to the amp. the wires are 1/0 gauge wire with heavy insulation, so they are fairly big.
im going to be running 2 15" 2500watt rms wardens from incriminator audio. the amp i am going to us is the Crecendo audio BC5500D that runs at 5800rms at 1 ohm. and i have a 105a mechman alternator. all the wires are form Knu Konceptz.batteries are from XS power.