Glad I found some other people that had the same problem with the loose battery cover. I thought I was the only one!
I went down the apple store to check the display models and all of those battery covers fit tight. I have an appointment later today too get my cover checkout.
Here is video of my loose battery cover.
http://www.youtube.com/watch?v=lbzx--isKN8
Thanks for the video -- sorry to see you're having that problem