Originally Posted by 2planker
Looks like its 1/0 or 2/0 best I can tell
If you are not 100% sure, then it is best to assume they are the smaller size or 1/0.
Comments on your electrical layout:
You did a nice job of planning and placement!
Nit: Where you mention combining the batteries, they form a 210Ah battery ... your diagram has 210A.