[Healeys] Battery Chemistry

[JACK NEWTON]

I have an unusual situation with the positive battery terminal as it 
connects to the ground cable on my recently restored BN-2.   Over a few 
months the helmet terminal grows a very thick cover of bright blue-green 
corrosion (looks like mold)
which gets up to 3/8 inch thick.  I have had to clean this much off on at 
least 2 occasions.  Any ideas on what could cause or prevent this?  I use 
the green and red felt discs on all terminals and 3 stay clean but the 
problem persists on this one!
Jack