A reason for over-charging is most often related to using a single mode converter/charger setup that constantly puts out 13.6VDC charge voltage. This amount of DC VOLTAGE is right on the edge of making a battery boil out the battery fluids if left on charge over time. When the fluid levels drop below the internal cores than the battery is prone to shorting out and really drawing alot of DC current which may result in an explosion.
If you have such a converter/charger it behooves you to check your battery fluids on a regular basis, A good fix for this is to purchase a good smart mode converter/charger setup for your 1994 MH.
Just a thought here....
Roy Ken