I have two 6 volt Trojans hooked in series in the camper. They haven't been out since being installed six years ago.
I use a Battery Minder Plus. It gets hooked up usually mid Oct. and stays there until the camper comes out for dewinterizing some time in May. It keeps the batteries charged, and desulfates them at the same time.
Using this, I haven't had to remove the batteries during the winter. There has never been any over charging, never had to add water during the process.
It's the best setup I have found and I'm totally sold on that particular Battery Minder.
As stated previously, if power is interrupted/stopped/disconnected to the battery minder and it's not restarted, it will drain the battery.
Instructions advise to use it when ever the vehicle is not in use. You can never over desulfate.
2008 Cruiser CF26RK
135 Watt Solar Panel
2013 Ford Eco-Boost
Heavy duty payload - Max tow