I picked the fifthwheel up from the dealer today. They did some work in March and left the battery disconnect on. Well when they brought the camper out the batteries were completely dead. As in no power and not even a light would work.
The dealer plugged the camper in and after about 1/2 hr there was enough power the landing gear would raise the camper up high enough I could hitch up. By the time I arrived home there was a 1/4 charge showing. That is the first time that I know of that the batteries were completely dead. We do boondock and have had the batteries get low before but never dead. They are maintenance free batteries. So I can't check water levels.
I generally try to replace stuff like batteries and tires before they fail.