You have raised a REDFLAG mentioning water present under your batteries.
The 13.6VDC is right at the level that causes battery fluids to boil out. You really should be using 13.2VDC for long term trickle charging. If you can only use 13.6VDC then what you should do is to watch your battery fluids levels real close. Once a week at first to see if you are losing fluids.
If the fluids get below the cores internal battery failure may happen.
Keeping your batteries re-charged using the smart mode chargers will take care of all of this for you. I would still check the water levels anyway haha.. I can't afford to replace my batteries...
Roy Ken