Going back to the original question on isolating the battery from charging after fully charged. I currently have this installed on my van, this gives me total control over my system. This was somewhat prompted by the possibility of moving to Lithium batteries.
I put together a google slide show to run through the reasoning of this.
https://docs.google.com/presentation...it?usp=sharing
Please let me know if there are issues with the slide show.
-greg