Water evaporates from SEALED car batteries!

I have a sealed battery that is 3 years old. It lost its charge. I
pried open the top plate which covers the cells (with a screwdriver)
and squirted water into the cells. I then glued back the top plate.

The battery works fine now.

Anybody tried an easier way - like drilling a 1/4" or 3/8" hole into
the top plate into each of the cells- filling them with water, then
sealing the holes with clay or polyethylene plugs?

 

I would check the charging system to make it is ok.
Water evaporating through the vent holes is usually an indication of
the battery being overcharged.

 

It is kinda normal and charge discharge cycles and high temps can
aggrevatte it. Even sealed batteries are vented to releive pressure
and gas from building up in battery. They add calcium to plates to
minimizing gassing in sealed batteries but sometimes they run out of
water before they end their life otherwise. Myself if I get 3 years or
more out of a battery and then it fail me, I replace it because new
battieries are cheap insurance because once a battery has let you
down, it will again, the only question is when.