This could also be a sign of battery faiulure big time. If the battery shorts out a cell the converter really has to pump in DC current to try to get the battery voltage up again. Need to check your battery fluids as they may have been boiled out on you...
You need to disconnect shore power and read your battery terminals.. If the battery is full it will read 12.6-7VDC... When you plug into shore power the battery voltage at the terminals should jump up to 13.6VDC or whatever other mode the mulit-stage smart mode charger is in... 14.4 etc...
If you disconnect the battery and just run off of shore power your DC voltage output of the converter/charger should read the 13.6VDC or maybe it may drop down to 13.2VDC... I have found the battery bank connected all time when on shore power or generator is a good thing for the converter/charger unit as it acts like a big capacitor keeping the DC voltage levels stable...
Need to have one of those inexpensive multimeters from LOWES WALMART around just to measure things with like this... The cost less then $20... One time one of the hardware stores gave you one for free with purchase of other items.. Harbor Freight I thing it was...
I use the PD9260C converter/charger unit with no issues... Works great... Have never been around the PD4000 series converter/chargers.. The PD4600 series is much like the PD9200 series... If you have two batteries in your bank you need to have a 45AMP charging system... Four batteries you really should have a 80AMP system But I manage ok with the 60AMP system I have... Just takes a tad longer to charge starting out with just 60AMPS verses 80 Amps I guess...
Roy Ken