After a fresh install the problem seems to have been resolved.
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9.04 power usage skyrockets on battery
https://bugs.launchpad.net/bugs/358136
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I've applied the modifications that are suggested here to boost the
battery performance: http://ubuntuforums.org/showthread.php?t=847773.
This causes the power usage to be more acceptable when on battery. So
more than likely gnome-power-manager is defaulting to some poor settings
when on battery.
