If you look down into the deep cycle battery cell hole you can see the bottom edge, as long as the water is not above it; and covering the plates you are fine. As the battery charges this prevents the gassing from spilling the acid all ovet the compartment causing corrosion. Keeping the batteries case clean also helps the life of the battery and don't forget the terminals connections. Well kept batteries I have seen can last up to 6+ years. Irover
You might want to check to see how much water you need in the battery. You can flood some batteries by adding too much water and it really reduces the ability of them to hold a charge. After I flooded a new interstate deep cycle I found out the water level was supposed to be just about a half inch over the plates. Not up to the bottom of the holes.
Yup, the water should not be touching the bottom of the holes otherwise you will get gasing as Irover stated. I plug in my two Interstate 6-volts in May and disonnect them in November and I have always been fine with the water level above the plates. I top the water off in November and put them on charge for a few hours.
2009 Holiday Rambler Admiral 33SFS (34' 3")
2008 Jeep Liberty - North Edition (4x4 auto)
FQCC/Camping Quebec, KOA, Good Sam, Coach-Net