When wmbattery is emerged, its graphics files are put in /usr/share/pixmaps/wmbattery. When the app is started in any other directory, it complains about not being able to find smallfont.xpm. The ebuild should know to configure wmbattery to look at the right dir to find its images and fonts so that it can be executed from any working directory. The requirement of running this dockable app from a particular directory makes it difficult to have it automatically run in some X-windows configurations (I am using KDE with Fluxbox, and trying to get fluxspace to run wmbattery when it starts, but that's not important here).
In case anyone else is having this problem, the simple fix is simply to make the folder /usr/share/icons/wmbattery/, and put all the *.xpm files in there. The ebuild does need to be fixed though so that this won't happen.
Fixed with new revisions, thanks for the submission.