About 15 years ago I had a weird situation on a M52 where i was using it a couple days a week in winter thus i rarely disconnected its ground cable.. Went to start it one day and they were deader than dead so they got swapped out and all was fine.
I discovered one battery had shorted plates , but when i put the other 3 dead ones on chargers, two were taking just fine but the 3rd battery sparked like mad when i attached the final alligator clip.. I double-checked my polarity and it was correct, but it still sparked like mad ..
Just for giggles i swapped the clips around, expecting a REALLY big spark... But no spark and it started to take a reverse-polarity charge (!) .. Never had seen this before but google can be a good thing sometimes... I soon learned i wasn't imagining things, this was a real situation others have seen, learned how to get the polarity restored on a battery, and it worked..
Apparently the internally-shorted battery drew all the others down and somehow made one of them go into reverse polarity .. So weird ! .. Has anyone here seen this situation?