The battery on my '88 Westy (54K miles), seems to be slowly losing voltage over a few
days, recently. Hasn't gone dead yet and starts right up. It sat this summer for 7-8
weeks, and started right up, no problem.
The battery is 2.5 years old NAPA brand.
Alternator belt is good and proper tension.
Alt. output is 13.9 Volt, at the large stud and 14.0 at the smaller one below it.
Voltage at the battery with engine running is 13.9.

Do these figures sound about right?

Looking at the electrolyte level, it was just covering the plates, so I added
distilled water up to the ring at the bottom of the hole.
Forgot to check the Sp. Gravity, but I noticed that the  gray bar across the top of
the plates is clean and sharply defined in 3 cells, but in the other 3 cells, it looks
black and gray and crumbly. What am I seeing???

Thanks,
Jerry