It depends on what you are doing and how your doing it. I can disable wireless and plugin, unplug all usb ports, turn my screen down and websurf for 2 1/2 to 3 hours without a problem on my 9-cell. I've been able to play Soldier of Fortune 2 on-line with a USB mouse on wireless with LG screen turned down to the 2nd lowest setting for 1.25 hours which surprised the hell outta me actually! Now if I turn the screen up all the way I'd be lucky to play 40 minutes.
Edit.. Ohh I've been able to play a full 90 minute movie on 9-cell with brightness turned down 1 setting only. Still had a bit of time afterwards left.
With wireless enabled, screen at 3/7, and browsing, I get about 2.5hrs (but I got 2!) on my 9-Cell. However, I do have a 7200RPM drive, and sometimes play music softly.
I also have an external mouse as well, which takes some power.
I get about 4 hours with my 9 cell. but i switch up tasks like gaming(1hr), web browsing (2 hours), Listening to music and utilizing apps(word) another hour. I was doin all that on my 6 cell and was only gettn 2 1/2 hours.