Splitting up the batteries and charging

So I did a pretty darn thorough maintenance of the two 6v Interstate Batteries on the trailer. They are right at 2-1/2 years old. They've been run flat three times. By flat, mean they would not light up a test light...........pretty darn flat. When I checked them out at the earlier part if the year I had them unhooked from the coach, charged them fully, let them rest and they all had good cells according to the hydrometer. Today there was some corrosion, but not bad, and all connections solid. They seemed to be fully charged at 13.31 volts, but one cell in each battery measured below the "good" and was in the "fair" zone of the hydrometer. It was on the upper side of fair, but definitely not in the green. When I hooked a charger up to the battery, it says the batts are full and the needle just bounces around like it does when the battery is fully charged. The only other place to look is where the 8ga. wire goes to the "line" side of the converter and I found that the lug where the 8ga. wire connects was loose. Not sure if it was loose enough to cause the issues I experienced last week end, but I'll tell you, it was anything but tight for sure.

We are heading out for a week toward northern California Coast next Friday and I will see how the dude works with the lug tightened.