Dell e6400 loose 9 cell battery

I have not seen 1 Dell laptop with a battery that sticks out that is not loose.
Don't worry, it won't fall out. If it was an issue, then it would be on reviews.

It's loose the same on both sides to me. Are you sure it's not just you that is imagining problems? Anyway, I say, if you are not comfortable with it, contact Dell about it so that they send you you a replacement one.

 

As for the battery, I think you're good. If it was a perfectly tight fit, it could be a major pain to take out and put back in.

If you think that cover is loose, there's an easy way to check. Remove the bottom cover (1 screw in the center), and then remove the screw near the DisplayPort connector (on the outside of the computer). Then you can remove the part and try to reseat it so it fits better.