The shade thing is really the reason we have not gotten solar panels -- as native Southern Californians, we crave shady places (and trees) because they are exotic and refreshing -- we actively seek them out and will usually refuse to camp in a sunny spot, unless there is no other choice. (We get 300 days of bright sun per year at home in Orange County.) Portable solar panels are an option, but then you have the hassle of deploying them and packing them up, just one more chore. Plus they take up room in the truck bed.
So we will probably stick with our system of two batteries, one as a spare, knowing that this shortens the useful life of the batteries (as NinerBikes correctly points out).
Life is a series of compromises. Almost no solution is ever perfect. (Except for folks who usually camp in sunny places!)
OK, I'm off to try my "freshening charge" for my new batteries -- it looks like I will essentially be running an equalizing routine, using the 8 amp DC output from my generator and monitoring both the amperage and the voltage as best I can with my multimeter. I sure hope this won't harm the batteries, but nothing that I have read indicates that it will. And several manufacturers do recommend this procedure.
The only problem is that once I am done with this process, there is no way to know whether this has really improved battery performance. I don't have a "control group" -- to do this scientifically, I should freshen one battery but not the other and then compare their behavior. But I am not going to do that, since I want to treat these twin babies equally so that they have identical lives.
