A lot of the aluminum mb and mbps have loose battery covers but that does not make it normal or acceptable. My mbp does not have a loose battery cover and neither did any of the mbs and mbps I've seen in stores. If it bothers you, I think there is some way to fix it by bending the clips.. or you could take the book back to the store and swap it, or just live with it if it doesn't bother you that much.