I isolated the batteries by wiring a seperate fuse block ($12) to a costco deep cycle group 72 that is charged by my Honda 8 kicker (puts out 5 amps) and runs all the accessories that may run my battery dead eg; lights, stereo, amplifier, cigarette lighter adapter etc...

For starting the 302 I have an Optima gel starting battery, also from costco, that runs the starter and critical acc like bilge pump, wipers, sounder, etc...

works great

I can charge or jump either battery with jumpers if need be.

ps; I choose to wire the electronics to the starting battery because they use so little power and that battery is always tip top while the deep cycle may get run down after I pass out and leave the stereo on or something like that and a run down battery is not good for electronics.