Today I received a new battery for my Dell Latitude E6400 laptop. The old battery (a 6 cell one) only lasted for about 15 minutes any more, 1,5 year after I acquired this system. The new battery is a 9 cell version. gnome-power-manager estimates I should be able to run 6 hours now without a charge, which corresponds with what I expected.
Now that I have a new battery, it is time to take a look again at trying to lower power consumption as much as possible. On my system I am using Mandriva 2010.1 Cooker with GNOME 2.30 and laptop-mode-tools 1.54, but this howto should apply (sometimes with slight modifications) to other distributions too.