I have 12V system (closed type acid batteies) 30 days ago left the marina with %100 First 3 days long sail 8h a day so it was always %100 then we stay anchored not always suny .Now my system early morning goes 11.7V- 11.8V and after having october sun end of day reaches 12.6V but system shows %85 Is it normal .Why it does not go %50 % 49 etc since during night voltage is under 12 volt.
Voltage only gives an idea of how much charge is in the battery. Especially when it's under load, under charge or it has recently been under charge or load. For that reason the monitors measure current into and out of the battery and use that to calculate state of charge.
If your batteries are old/getting tired, then the capacity reduces. In this case the state of charge based on the battery size will be wrong. So, for instance, a 100AH battery may only store 80AH charge.
If your battery capacity is correct in the monitor, good chance that the batteries need replacing.
