My Coachmen Freedom express has been plugged in since I de-winterized it in April, the battery (new in 2014) was stored in the garage (heated) over the winter. Over the last week I've noticed a sulfu...
I have had RVs of one kind or another continuously for the last 15-16 years. I have always left them plugged into shore power and have had no battery issues. Leaving your RV connected to shore power should not cause any battery problems. I've had in water stored boats almost as long and no problems there either.
You have either a charger problem, a bad battery or an improperly maintained battery. You could have all three.