Well, when you KNOW your batteries are not getting to 100% each day, you sure don't need to check SG. I have no use for one myself.
After a couple weeks when battery performance is lacking because of the 80% charges, I mite use the little genset for a couple hrs one day, then let the solar take them to 90-100%, and I'm good to go for another couple weeks. I don't care much about 100% all the time. And when I get back home and on the grid, the PD makes them like new again.
My 12'ers are near 6 yrs old, doing great,........and w/o a hydrometer !