Battery Low is to trick your acquaintances by thinking your battery is dead (or charging).
Just press the play or center button to display the image. If you hold the play and hold buttons together, the charging symbol comes up. You can hit the lock button with the image on the screen, and the image will stay there.
And thanks to pokeyourheadoff, the pictures look exactly like the zune original.
You can find
screenshots here.
The download is:
CCGAME
Source Code
Good luck!
License can be found at
http://www.gnu.org/licenses/gpl-3.0.txt
Edit:
The image in this app is not the Zune 30.