I using my MacBook Air (original) and all of a sudden the trackpad button stopped clicking. I also noticed the front left side of the Air started getting increasingly hotter. I raised the Air to eye-level and noticed the top and bottom case was expanding and growing. Realizing that my Air was about to split in half, I immediately opened it up and discovered my battery was blowing up. I removed the battery and set it aside.
The repair went very smoothly, easy swap and the Macbook booted up properly.
I was particularly happy that iFixit included the fact that the Macbook Air Mid 2009 battery worked in the 2008 model. Giving me more battery capacity at the same price.
If your Macbook Air starts blowing up and is outside of warranty, open it up ASAP. Otherwise the battery will surely break all of the rigid components inside that can't handle the expanding pressure. I was able to get the bottom case to return to original state by putting it into the freezer for a few hours.