It has been known for many users that a constant 13.6VDC charge coming from the converter/charger unit will drain your battery fluids over time. Works great if you constantly keep an eye on the battery fluids.
If this is what you have it would be wise to purchase a working smart mode converter/charger unit. The smart modes changes from 13.2 to 14.4VDc modes of operations automatically and keeps the batteries from boiling out their fluids...
I too have my trailer hooked up all the time here at the house using my PD9260C Converter/charger unit as battery maintaining source. My GP24 batteries on this trailer originally purchased in 2008 finally started to showing low performance last season (Won't hold the charge for too long of time)... Not bad for nine years of service and a whole lot of 50% to 90% charge state cycles as we camp almost all the time off-grid.
We always keep a close watch on the batteries both here at the house and on the road off-grid somewhere...
Roy ken