Your converter is overcharging the batteries causing the electrolyte to boil off leaving the batteries dry. If the battery is dry then you will need to replace it with a new one.
99% of the time when a battery is dried out it will no longer take a charge.
2007 Surveyor SV230 - 200 Watts Solar/MPPT Controller - 230 AH Battery Bank - 600 watt PSW Inverter - (2) 2000 watt Inverter Generators - LED Lighting - Boon Docking 99% of the time.
2009 F150 - 5.4 Litre - 6 speed - Tow Package