I realize this is an older thread, but it is spot on to what happened to mine. I got it last week and all was well. As I had many times before I changed the battery and all of a sudden it started to smoke and the battery got very hot. I popped out the battery and set it at a distance to cool off. The unit itself was not hot and the contacts were clean and dry so I put another battery in and there was no power. Oddly, if I put the battery in upside down it would power up just long enough to read that the battery was dead, though it wasn't.
My plan now is to take it apart and see what wires are crossed. On the other hand, it was the first coil I made and maybe that was it, though that same coil worked just fine for a full day. So anyway. It's not just you.