Gjac, that is a great idea about testing the hydrometer on distilled water -- it might be giving me "fake news" that all my cells are great when maybe they aren't! ;)
Someone mentioned that I am obsessing about my batteries. Guilty, with an explanation. We do a lot of boondocking, so if my batteries die, that would be a hassle. (Not a tragedy -- we would just pack up and go to an RV park.)
So although I am by no means a professional battery person (unlike a few of our members -- hi, Mex!!), I am always on the lookout for signals that my batteries are on the way out.
These are five year old marine batteries -- they have never dropped under 12.1 volts, measured while resting. Always topped up. Not a hint of trouble so far.
Based on the consensus of the posts above, it looks like I should not worry about a tiny drop in the water level of one cell over a period of several months.
And someone wondered whether I really meant that it was down by a half ounce. That's really true. I measured how much I had to add to the cell to get it up to where there is a "meniscus" at the bottom of the fill tube. That's the curved lens shape on the top of the water.
I have been told that you add water just until that meniscus appears. If that's wrong, I am sure someone will let me know!!
