When g-p-m wants to notify me of something (like battery being fully charged) the popup has a 'missing icon' image, the red X. However calling: notify-send -i gnome-dev-battery "foo" "bar baz qux" shows the right icon.
the same is true for Rhythmbox, bug in libnotify?
might be buggyiness in our weird, non-standard notification stuff. Either way, the problem disappears by symlinking one of the icons in %{_datadir}/gnome-power-manager to /usr/share/icons/hicolor/24x24/apps (and updating the icon cache).