Possible Duplicate:
Two battery indicator symbols, how do I get rid of one?
It seems there is a bug that displays an extra battery monitor in Oneiric. From what I found, it is not right in the panel, but in the wallpaper. Please the following images:
Best Answer
What you are seeing is not a battery indicator in the wallpaper. When you go into expo mode, any old notification-area icons show up on top of the wallpaper. You can report a bug on launchpad against gnome-power-manager, but it is likely that your problem is only temporary and will disappear with updates.
If you still get the problem, you can revert the whitelist settings for the unity-panel (unless you still need to see some particular application there).
BTW I have this problem in 11.10 as well; but I believe it is only temporary as it only appeared in the latest update I installed (so it will be gone before release).