How can I get my battery level to display in the notification area (system tray)?

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http://askubuntu.com – I'm trying to use the Awesome window manager with GNOME, i.e. running gnome-session --session=ubuntu on login, and it works great for the most part, except for the fact that the notification area/systray is missing a battery indicator. There's the Network Manager applet (nm-applet), a keyboard icon for switching keyboard layouts, but no battery icon as I would've hoped. I thought the command would be something like gnome-power-manager, (HowTos)