My dad taught me about exploding batteries when I was just a little kid. I was standing behind him watching as he was charging a battery.
He disconnected the charger cables from the battery after charging then touched a crescent wrench across the posts to see if it would spark.
It did......the top blew off of the battery blowing acid all over the place, he spun around and ran slap over me as he made a hasty retreat.
It was a great lesson. I have treated batteries with respect ever since. My dad was always a good teacher.