Today, when I was checking a terrarium for more baby Centruroides flavopictus 2nd instar scorpions to be moved to a container of their own, I suddenly heard a very loud plop, loud enough to hurt my ear. Esme and her mother were down in the livingroom and heard it as well. At first I had no idea where the sound had come from. Esme and her mother told me that it was coming from where I was standing.
In my hand I was holding the Portable UV light source I had made the 13th of Februari out of the UV LED scorpion detector I had made quite some time ago, and some additional electronic components. I had used two 9V Duracell alkaline batteries as a power source.
When I looked at the UV LED scorpion detector, I noticed that one cell of one of the two 9V Duracell alkaline batteries had exploded... So this was the source of the very loud plop. Each Duracell 9V battery contains 6 cells, 1.5V each. And for some reason one cell had exploded with enough force to push out the piece of metal that closes the bottom of the battery.
The exploded Duracell battery was not hot to the touch, otherwise I would have noticed that something was wrong much earlier. I have no idea why this battery exploded. I am quite sure it's not the circuit I am using, I have been using this set up for over 4 months, and I've had the UV LEDs switched on for a longer time than today as well.