Size of Wire to run?

I'm Locating two batterys under my bed. What Gauge of wire do I want to run from the batterys to the motor?

I'm only going by what I've seen done in audio vehicles and stuff but I would run 1 gauge wire, when it comes to power bigger is better and that's the biggest I've seen/had.
I'm no electrician though but I know with mains power the longer you run the wire the less power you have at the end, kinda like a garden hose (hose too long = low pressure) , but a bigger hose(wire) will carry the pressure(power) farther.
Don't forget you only need to run the positive back to the engine bay and earth the battery straight to the frame, you'll need to earth the motor to the frame too don't forget.

2GA min. for runs over 10ft...

I would use #2 welding cable if I was you! Way powerful and very flexible. That is what I used when I relocated my battery...

good idea never thought of welding cable.

ive done lots of large stereos, and the min. you should use is 2gauge wire, also make sure you put in a fuse atleast 150amps

welding wire works great im using right now for my stereo, and my air setup, it also can take a higher ampreage, just make your you get good connections for it