[J Witt]

Bigger is better for starters. 2/0 is good and not too hard to get proper connectors.

Incidentally, maintaining low resistance connections for high currents is important. In building electric vehicles, I used a compound called Noalox which is a zinc filled grease that excludes air and reduces corrosion, on all the battery terminals. Noalox is intended for alminum wiring connections, but I found it seemed to help keep battery terminals in good condition.

I don't have any data on this other than personal observations from making hundreds of high current connections.