As I said in my previous post, the method I am using is not the best for everyone. My battery usage is moderate & one battery is enough for my needs 90+% of the time. When my #1 battery stops having enough capacity to do the job, then it is time for replacement. My second battery is mostly just carried as a back up. My charging is done either from a loop on a small outboard or, more often, from a ProMariner charger that plugs into 110vac. The shoreside charger has battery isolation. I use either #1 or #2, but I don't use Both on the battery switch, except on rare occasions, when charging from the outboard or a portable generator. #1 is my working battery. #2 is my emergency back up battery for the times when I goof & leave #1 loaded for too long & it gets drained to the point where I can't use it immediately. #2 is little more than a safeguard against my forgetfulness. My method works well within the narrow confines of my specific needs.
I have read some of what Main Sail has posted, but I have not had the time to read the vast majority of the information that he has been kind enough to provide. I find very little room for even mildly dissenting rebuttal in the posts that I have read from him so far. He seems to be the very best practical battery-information resource that I have encountered, bar none.