I released the magic smoke from a robot battery
Someone took the 2 batteries out of the cardboard box, then put them back in the KOP box with all the METAL. I went to get the batteries (ironically to put the connectors on the terminals and cover them with electrical tape), and a piece of steel cable fell over both terminals on the battery.
I had to leave the room coughing for a while....it probably had to do with me standing over the arcing battery trying to get the cable off with my foot..