This is my favorite one on a customers car - Optima yellow top, very old
Went to undo the nut and that happened, can see all the fuzzy stuff below the terminal even though its an AGM battery
Optima yellow top is crap btw - Deka Intimidator is where its at for AGM (Its 9A34/9A34R are the ones for Falcon/Commodore, can't remember which is which though).