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.