You may want to look at your MH converter/charger unit. Being a 2002 model it probably does not support smart-mode charging technology and since you are on-line 24/7 this older series converter/charger will only produce 13.6VDC constantly. This is right on the border line of over-charging your batteries over time and will boil out some battery fluids. Once the levels get below the cores inside the battery then the battery starts going bad on you.
If you have such an older converter/charger then it would be a good idea to keep checking your battery fluids on a weekly basis or so just to make sure they are are not boiling out fluids.
Just me thoughts...
Roy Ken