While that works for some greg, for others its not practical and having redundancy on big water is always good.
I have a seperate power system in my boat for accessories.
HDS8, LSS-1, Sirius Weather and Radio, Amplifier, am/fm radio, Lowrance VHF radio, two power poles & pumps are all wired to its own fuse panel connected to a 24 series dual purpose battery. That battery is connected to a switch as battery #2 that will allow charging from the onboard 4 bank GUEST charger. The 24 series cranking battery (850cca) has the Ranger boat harness connected to it. That battery is battery #1. The outboard is connected to the switch also. So when the switch is on #1, the outboard cranks from cranking battery only and it charges battery #1 only. When the switch is on battery #2, the outboard will crank from battery #2 and charge battery #2 only. When the switch is on BOTH the outboard will crank from both and charge both.
I usually run it during a tournament with the switch on #1. When I charge it at home I switch it to BOTH so the chargetr can charge both. It works great and I have peace of mind that my HDS/Lowrance/amplifier components wont run down the cranker. Also note that I have a 225 EFI NOT an Opti. If it were an Opti I would have installed a 1000cca cranker.
I also installed 3 50amp circuit breakers. One for the cranking battery, one for the "house" battery and one for the trolling motor batteries. All breakers are shut off during charging so no damage or spikes can get to my electronics.