The best idea is to just stop worrying about all that stuff. If you have a continuous battery voltage monitor, just watch it as the day or days progress. You will develop a pattern and learn to live by it.
In my case, I bought a two decimal point voltage meter from China for about $3 delivered. I connected it to my battery so I could see what it said. I learned to watch it roughly to see how fast it fell, and learned to top up with generator as required.
Now I have tons of solar, so I never have an issue with our usage.
