There is only one way to accurately know what your battery banks (SOC) state of charge is and that is with a battery monitor that measures the goes into and comes out of.
http://www.bogartengineering.com Trimetric and http://www.victronenergy.com/battery-monitors Victron. One of these will also give you a handle on vampire loads and actual use.
As stated earlier not reaching 100% SOC with regularity is the passage to a quick death for expensive batteries. Measuring voltage other than after 4+ hours with no load or input will give a false reading (high) so your SOC is even less than you think.
As a former tenter I do appreciate your consideration I hate listening to some ones generator which is the reason we went solar and the generator stays home, except when we anticipate the need for AC.