Well recently I've been trying to charge a number of old maintenance free (MB specific) batteries that have been sitting is cars (terminals connected) for sometimes years. These things can be up to $300ea so there was a fairly high desire to resurrect at least a few. But no dice...
I have two full size chargers and each one refused to flow any current through the batteries, even after many hours on the high or low current settings. I wondered if the plates were getting coated with debris...