Re: Charging / Discharging issue
I agree with everyone else's and your assessment that something is not right. Get yourself an inexpensive Battery Tester like this one: https://www.amazon.com/BA7-100-1200-Electronic-Battery-System/dp/B0015PI7A4/ref=sr_1_1?ie=UTF8&qid=1525809987&sr=8-1&keywords=solar+ba7
It's not a "real" load tester that a professional marine electrician would use. However, I have one and was able to compare it's results side-by-side with a real load tester when I purchased my new batteries last year. The results were very close (within 5% or less) to the "real" load test results. Certainly close enough to see if one or more of your batteries has an issue and is compromising your whole battery bank. I would get one of these ASAP and test each battery.
Also, you really can't trust the "% of Charge" on your battery monitor for much. Here is a very long and detailed article as to why: https://marinehowto.com/programming-a-battery-monitor/
SM #440 Cara
Deale, MD USA