iPod battery grows a fat belly as it gets old

We bought a U2 special edition 20GB iPod back to 2004, it was expensive comparing to today's iPod lineups. It was used with a dock station in Benjamin's bedroom for playing Baby Einstein when he goes to bed. A few months ago, the round button in the middle stopped working, I couldn't press it. It feels like a mechanical issue. This morning I took the a knife and screw driver, and opened it. Guess what, once it was opened, the middle button started working.



So I closed the case, and the button stopped working again. After reopen it, I realized that the middle button sits on top of the battery, and the hard driver is underneath. See the picture:



Over the time, the battery changed its shape. Isn't it like most of human beings? when you get old, you get a fat belly. ;)
Fix was easy, I peeled off the sponge pad on the back of the hard drive, so it leaves some room for battery's fat belly. With a little surgery, my old iPod is back to work again.