A numer of years ago I was trying to get one of our excavators to start-it had a flat battery. I went into the workshop and took off a large battery that was on charge and wondering if it was fully charged or not decided to use one of those rapid dischage things with the 2 prongs attached that you brigde the battery with
Needless to say that as soon as I touched the battery it blew up sending the glass ball things through the steel roof!!
Thankfully as Willik can confirm it didnt spoil my good look
, but it did make me repect batteries a little bit more.