I have one of those idiot LED "level" indicator panels for my three tanks and
the battery.  I refer to them regularly knowing full well that what they
indicate are no more reliable than a WAG.  That said...

When I am connected to shore power, the battery indicator reads [full].  I
consider this nominal.  When disconnected from external power, it reads the
battery level reliably, if not particularly accurately.

The last time I was running off the battery, when the level indicated 2/3, I
fired-up the genny to recharge the battery.  FWIW, I have a 40A aftermarket,
nice converter.  I noticed, however, that the state-of-charge LEDs on my
<koff> panel were not all illuminated - as they normally are when connected to
the grid.  It seemed to be reading the battery even though there was shore
power.  To my dismay, I discovered that, for the first time, two hours of
generator time did nothing for the battery.  All the time I was running the
genset - and running water, burning lights - I was depleting the battery.  
Interestingly, the microwave worked off the genset.

During this anomaly, I reached down and gave the old, factory converter (now
using only the 12VDC distribution section and, I suspect, some switching) a
good thump.  The LEDs then all read full and the lights brightened.

I suspect that the relay (or whatever the device is) that automatically
switches between shore power and battery power is acting up.

History:  When the factory converter (Centurion cheapie) went up in smoke, my
trusted  friend and RV tech replaced it with a nice converter.  (~$170 part
w/smart charger module about 2-3 yrs ago)  We retained the Centurion "front
end" with its 120VAC breakers and 12VDC automotive blade fuses.

I found out the hard way the last time I was "on the battery" that this was
happening.  After running the genset for a couple hours, which usually will
bring a "2/3" indication to "full", I noticed that the state-of-charge hadn't
changed.  Then I discovered the relationship between the LEDs and a good
"thump" on the cover of the old converter.  It's happened twice so it's
reproducible.  What's going on?  TIA.