After reading your post at my local time ~ 14:00, i unpluged my laptop from power.
Was watching a movie whiel browsing the forums, so i finshed watching the movie: about 30mins.
However, F15 was claiming to run on low battery just from the moment i unpluged the power.
I ignored that.
For some reason i wanted to reinstall F15 after movie was done, done :P
Copying 7.7gb of a dvd to local drive, wrote a guide, and downloaded like another 1gb mainwhile.
Anyhow, during about 2.5-3h F15 was telling me i'd run on low bat, the time i really had a low bat (less than 25%) it was still running fine, allthough the screen was darkned after like 50% battery power.
Do you experience REALLY low battery life (fast power drain), or do you refer to the error message?
PS: Anyhow, WiFi does eat some amount of power, rather than wired internet which i used.