When my batteries drops below 12.0VDC which is approximately 50% charge state I will re-charge them. I usually leave my battery bank connected but the trailer is plugged in to my 120VAC 20AMP service coming from my garage during the winter months. Using my smart mode CONVERTER/CHARGER almost takes cares of the batteries automatically. I will however check the Battery voltages and look for boiling out of fluids.
My batteries will drop below 12.0VDC in a short time being drained by the parasitic items in the trailer if not connected to shore power.
It has been my experience that if the BATTERY drops below 50% charge and not be re-charged right away to at least 90% charge state then it will not perform as expected. Continuing to be drained below the 50% charge state will eventually do harm to the battery and will have to be replaced.
Even if you pull your batteries they will will loose some charge. I would keep a close watch on the DC VOLTAGE levels measured at the terminals. ALot of folks will keep a small battery trickle charge or solar panel keeping the disconnected batteries up to par over the winter months.
Simple Battery Maintenance is must do thing here.
Roy Ken
My Posts are IMHO based on my experiences - Words in CAPS does not mean I am shouting
Roy - Carolyn
RETIRED DOAF/DON/DOD/CONTR RADIO TECH (42yrs)
K9PHT (Since 1957) 146.52M
2010 F150, 5.4,3:73 Gears,SCab
2008 Starcraft 14RT EU2000i GEN
2005 Flagstaff 8528RESS