How do I know what size cable to use in my system?
When talking about Cable sizing there are a few factors to consider.
First, what is the size of the load you are power with the battery bank?
Second, how far away from the battery is the load? You can do voltage drop calculations to see if you need step up your cable size.
As a rule of thumb you can use these numbers as a guideline.
4 AWG wire approximate max rating is 157 amps DC
1/0 AWT wire approximate max rating is 291 amps DC
4/0 AWT wire approximate max rating is 456 amps DC