Engadget had the same problem with their review model. If you can the easy solution is just to take off the back and stick down the battery properly.
Interestingly, the back plate peels off, should you need to swap out batteries or just take a nice long look at the internals. In our case, we had to pry it off to find out why the reader had a strange rattle to it. Turns out, the battery had become unseated during shipping.