I had one here that was going somewhat wacky with odd characters appearing on the screen. I was able to determine it wasn't the screen as other things displayed in the same position were fine. We decided to upload the software again. However, it continued to go through the press the button, release the button dance, and finally we couldn't power it up at all. Obviously, I did check the batteries, I check on the contacts going to the electronics for full voltage from all the batteries. I can only surmise that it was having some processor issue, and when we started the firmware load, we finished the job.