Your trailer must not have the SMART MODE CONVERTER/CHARGER unit installed.
The converter/charger units that only puts out 13.6VDC are right on the edge of making the batteries boil over over time. If this is what you have you should be checking your battery fluids at least once every two weeks or even shorter time.
If you have the smart mode converter/charger installed (PD4600 or PD9200 series) then the converter will take care of the boiling out problem for you automatically...
My problem was I had the WFCO 8900 series smart mode converter/charger unit and it would never go into any smart mode charging. I replaced it with the PD9260C 60AMP unit as I have multiple batteries to keep charged. If you have one or two batteries I would go with the PD4645 converter/charger unit.
If your battery has been boiled out it is probably history now and will need to be replaced.
Roy Ken