The batteries used in the HD HERO cameras need to be power cycled a few times when they're new before you'll get the full battery-life out of them.

To power cycle your battery, please charge until full and deplete by recording a video with the camera.  Repeat this three times.  Your battery-life should then be about 2 hours of continuous recording.

If you continue to have shortened battery-life, please contact GoPro Customer Support.