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I have a question regarding off-gassing of antique car batteries while charging. If I have my batteries on constant charge with the tops off, would that cause enough sulfur discharge to corrode the receptacle terminals and cause copper wire tips to turn black? This is in a large, high ceiling, 2 car garage, in Southern Louisiana. 
Looks like oxidation. That will happen just from being exposed to air over extended periods of time
If copper is turning black in the atmosphere, the cause is very likely hydrogen sulfide ( H2S ) . Any chance of some leak from a nearby oil/gas well ? Although you should smell H2S at very low levels . Maybe a one time occurrence ? Copper is sort-of like silver; silver turns black due to H2S at such low levels it can't be smelled. I don't think a lead/acid battery has anything to do with it. In moist air copper will develop a blue/green patina ; a mix of hydroxides, carbonates and other stuff.
