I forgot to mention this. I've done this once or twice and it works. But I've heard not all brands of 9V's use AAAA's. Also the cell is missing the top button, so it'll look like you're putting them in backwards, and they need a small spacer. But sure if cheap.
I've purchased AAAA cells at Wal*Mart, Radio Shack, and Best Buy. They are there, you just have to look real close. Don't rely on a clerk knowing where they are - most of them don't even know they exist...:huh2: