My older converter setup only put out 13.6VDC which is right on the edge of heating up the battery enough to boil out the battery fluids over time. After I replaced the older converter/charger setup to a smart mode charging setup I have not had to add battery fluids anymore. Out of habit I still check the batteries but always seem to find them OK fluid level wise. The smart mode converter/charges uses DC OUTPUT voltages at 14.4VDC - 13.6VDC depending on the charge state. When the Batteries are completely charged the smart mode converter/charger will drop down to the 13.2VDC MODE which is a very safe DC VOLTAGE to keep the battery charge maintained and not boil out battery fluids.
Your 2010 Model trailer is most likely using a smart mode converter/charger unit or the DC VOLTAGE OUTPUT from the converter is lower than 13.6VDC.
Roy Ken