Which would be better?

[tooshort_128]

After years of doing car audio, I have acquired a ton of crap. So much that I have enough wire to connect my batteries, wire my amp, and do the big 3. I have about 20ft. of 0 gauge and another 20 or so feet of 4 gauge. The only thing I'm wondering about is which I should use to connect the batteries and which to sent power to the amp? So would it be more efficient to connect my batteries (both in engine compartment, about 8ft. runs) with 0 guage and use the 4 gauge to power my amp or vice versa? I was only thinking the other way and using 0 gauge for the amp since its a longer run.

[tooshort_128]

nobody? really? If its a dumb question, forgive me but I'm looking at the length of the runs.

[keep_hope_alive]

You are right to upsize for distance. 0 for amps, 4 for jumpers between batteries.

How many batteries? If you tie into a battery bank in the middle, you minimize voltage drop across the jumpers.