I wanted to be sure I had the maximum battery function for the used MacBook Air I purchased on eBay.
It was easy as pie - got the proper tools, sat down and followed the directions.
The chief advice I would give is to seriously observe the potential for creating more problems - specifically by detaching the battery terminal (gently) and then seeing that it does not fall into contact again while the screws are removed. I did this by putting a piece of paper over the attachment terminals. From there it was fairly straightforward.