Hmm, I found this rather interesting. I can't believer I've never dissected a 9-V battery. http://www.youtube.com/watch?v=tr5ZB1eFhwc
Yeah. I've known about that for quite a while. Also, 12-volt batteries such as the A23 have button cell batteries in them. I've opened one. I'm not too sure about their quality, but they worked. You have to be careful about which brands, though. Some may use smaller battery parts, but others just use a single container. You don't want to puncture one.