How long should my MacBook Pro battery last? I have brand new Macbook Pro (15", i5 2.4GHz, 4Gb RAM) purchased at the end of May 2010 and Apple advertises up to 7 hours of wireless web battery life, however I consistently getting only about 4 hours when I use it normally, i.e. WiFi is turned on and quite a few apps are running, but nothing too resource hungry like games or Photoshop. I tried to figure out if my settings are incorrect or if I'm using some apps that really drain the battery, but can't find any obvious issues, so I wonder what other MBP owners typically get from their batteries? Is 4 hours a typical or I need to replace my battery or do something with my setup? When Apple states up to 8-9 hours, must you turn off all wireless, dim your screen to the minimum and perhaps the only app running be Terminal?
It's likely that you are running something in the background (such as Skype) which is triggering your dedicated graphics card, despite it not actually doing anything graphically intensive. This is a known issue in Apple's graphics card switching technology.

Download and run gfxCardStatus and see if I'm right. If so, close the problematic program or use gfxCardStatus to manually switch to the much lower-powered integrated chip. You should get longer battery life after that; I haven't directly measured it but I know I get at least 30 minutes to an hour of extra life.

And of course it also depends on what you're doing with your computer, what background programs are running, the brightness of your screen, etc.