I would guess that your battery is dead, but somebody more experienced in this area would know much better than me.
Two things that may help:
1. If your battery isn't an original, check to make sure its contacts can actually touch the Z's. There is a thread dealing with this somewhere (Accessories?)...
2. If your battery is just dead, you could try putting it in a plastic bag in a freezer for ~24 hours, allowing it to return to room temperature (still in the bag to avoid condensation), then charge. This is supposed to revive dead batteries (I believe it gave mine an extra bit of juice, but I haven't done any tests, so it may be power of suggestion)
Anyway, good luck!