You can run the 2/0 to a block on the transom and then switch over to the factory outboard battery cables. Very standard install.
I used one of these in the transom with a 3/8 stud:
https://www.bluesea.com/products/cat...Dual_PowerPost
I looked on my Sceptre today and I guess I did end up using 1/0 from the batteries to the transom. Oh well, I thought I had used smaller stuff.
Ran the OEM Evinrude cables through the rigging tube and hooked them up to the power posts.
Engine has a dedicated battery. Used an Automatic Charging Relay to charge the house battery. Batteries are under the floor by the helm.