Re: Fusing Batteries
If you are looking to upgrade the 4 gauge wiring, I recommend genuinedealz.com for custom battery cables. The quality and price are both excellent, and I used the savings to upgrade the cable gauge a bit (both batteries now connected to the switch with 2/0)
Note that although your starter is 75A continuous, there will be a surge of higher current to get the engine turning over. This is when voltage drops in the cable can be noticable if the wiring gauge (or connections) are marginal. BTDT.
Bristol 31.1, San Francisco Bay