Outer Limits 4x4 Board

Well im making my own dual battery kit, using one of those boat battery isolator things,so far ive got

-i got the isolator
-a battery holder (and battery)
-beer to go in fridge when finished


i just dont know what thickness of wire to get to wire it all up.

id use 1 guage for the power and earth

same as what goes from you battery to the stater motor