Try the tricks in the How to Remove a Stuck CD guide.
These tricks seem to work better in CD players; not so well in CD changers. I haven't noticed a report from anyone about getting stuck DVD discs out, so please leave a comment here or at the guide if any of the tricks work (or if none of them do).
And yeah, it's suspicious that your battery acted up just before this. If you put a new one in, that's about the same as pulling the fuse trick mentioned in the guide. But maybe pulling the fuse will reset it.
Otherwise you'll probably have to visit a car stereo shop or your dealer. Good luck!