Battery Gauge Erratic Reading

HI.  I have a 2010 Duffy Cuddy 22 that I purchased a few months ago.  Batteries are from March of 2017 and were replaced by the previous owner but the boat never saw service. Sat in the guy's driveway and on a 110 volt circuit for the duration supposedly.  I have had it on 30 amp shore power ever since I bought it.  I have had it out three times with no i problems.  Upon turning the key, the charge gauge reads 19.9.  Under power, the gauge reads 6.0 initially.  After about 30 mins of running it reads about 5.7.  After about an hour of running it reads about 5.4 and after about three hours of running it reads about 4.9. From reading the manual, that all seems pretty much normal.  I should also mention, that on each trip we dropped anchor with the electric windlass for about an hour and then proceeded to head home.  Upon restarting the gauge still read what is said when we stopped. That was trips one thru three.

However, on the last two trips, despite the gauge reading about the same as the above when we start out, after dropping anchor and lunching for an hour, we once again weigh anchor and then begin to head home again, then the gauge reads "E" and says ".2"!!! At this point, we are at least an hour or so from home so we just press on.  In both instances, I have made it home no problem and have felt no diminution in power at all even though the gauge displays the .2 reading and is flashing the whole way back.  

Anybody ever experience this before?  Is this a problem with the gauge or is it deeper in the electronics of the boat ?  Charging system?  Seems not charging because we always have power? Is this something I should be worried about?  Obviously this is something I want to get fixed but we only have a few more local trips to do before we put her up for the winter and want to deal with it at that time it if can wait. 

Many thanks for any insights!