My Macbook has fine battery life if I'm just surfing the web but when I'm working on music in Logic it chews up battery like you wouldn't believe.
That's pretty much the same for every system - if you get all four cores (two if it's a MacBook) running full speed, it takes a lot of power.
One Latitude that I have runs from 6 hours (surfing/mail with LCD at 50%) to just over an hour (installing operating systems in VMs while compiling Visual C++ code).
Would you rather that it be dog-slow in Logic for 5 hours?