I use Ubuntu 12.10, but changed to the i3 window manger. It works great, but I do not get the normal "low power" notification. Notify OSD works as expected (I tested it per notify-send).
How can I activate low power notifications?
AFAIK ubuntu uses the gnome-power-manager (for power notifications), but this application isn't installed yet.. this is strange because If I login with unity as wm anything works!