Battery relocation question

I am going to relocate the battery in my car to the back. I have a 4 gauge wire from an old amp installation laying around. Do you see any problem using this to run from the battery + to the engine bay? If I can use it then it will just save me some extra $.
Thanks

You should also run a ground of the same size to the engine block, for the starte motor.

I think a #4 is adequate size, but I know if speaker wire insulation is up to the job of insulating all the amps this cable will carry at start-up.

4g should be enough for your battery, I dont think there would be any problems, I run 1 gauge welding wire to the back of the cargo area for my optima (kinda overkill but I like it that way.)