Just wanted to say thank god for this thread! This happened to mine after falling a short distance. I'd already tried wiggling the negative contact but it was jammed in there pretty much flush. I thought I'd google my problem before getting the precision screwdrivers out and found this thread. In the end, running my thumbnail around the negative contact made it pop out - but it was this thread that reassured me that it's a common problem that can be fixed, so thanks for that!