Common and many time exacerbated by the age old carry strap that clamps on both terminals and/or rough handling while tightening the cable clamps
Recently tossed my decades old post clamp battery handle after noodling this exact topic. Saw how it places high stress on both posts that messes up the post to case seal
Still see shops using that old style and think most of their customers will have compromised battery post to case seals
Bought a new carry handle from NAPA that looks like the old world ice block carry. This tool clamps on the side of the battery case and does not involve the post
I've always used dialectric grease on the post/case. Then a felt washer (they are next the batteries at parts stores) and the soak the felt with battery spray (also next to the batteries)....then the cable clamp, which I do not horse around so as to not mess up the new battery post seal
If the cable clamp has become stretched, either replace with new...or use copper tape wound on the post to increase it's dia
This is the tool.
walmart