When a friend told me that A23 batteries (a 12V type used in things like wireless doorbells) actually contain eight disc-type batteries (equivalent to type 394s), I was skeptical. After all, there have been urban legends involving batteries within batteries that turned out not to be true. Well, I happened to have an A23 battery on hand (in my doorbell button, actually), so I cut it apart to check. Amazingly, it’s true! Here’s a video….

This guy does a really nice job - I just took a hacksaw to mine (no video available).  More info on all this can be found here.