I did something along these lines two years ago I went away from the single switch to a system like described above (I think). One of the best moves I made. I still religiously check the water levels in the batteries but since switching I have not had to add water at all, before it seemed like a monthly event. I assumed this was due to them being combined all the time. I can now just turn on the house battery and listen to the radio without energizing everything.

I would be curious to your opinion on the system I went with Jim. I went with the BEP system, (716-SQ-100AVSR) which was very easy to install, it is actually made to replace a single switch and in most cases you can use your existing wiring. They have many different configurations, sing engine, twin engine, triple engine, two three or four battery banks.

Main reason I went with BEP was that was the brand of components that were already installed and they would mate together with what was already there and seem to be some of the smaller components on the market and space was at a premium for my installation.

http://bepmarine.com/Dual-Battery-Charging-Cluster-180-1464.html BEP Battery Clusters