Originally Posted by Rookie1337
I always found Windows to be both overly confident with battery estimates (not that Linux isn't either) and slower. The big point is that I've never had the battery life that I got in Windows; at the same time I didn't have as good of drivers or as slow of an experience. If you want to cut back a little you need to install cpufrequtils and then manually set the cpufreq driver to the powersave setting (It may require 2 tries to get it to stick after startup). Outside of that...backlights need to be dimmed and that pretty much all you can get to as a general user without having a prebuilt system from a Linux seller (I'd assume they'd have better control) or getting into some serious tweaking.
The CPU Governer is normally set to on demand which is generally the best i.e. speeds up when you need it and downclocks when you don't. The only problem then is when the CPU is being used it'll speed itself up, even if you aren't the one directly using the CPU ( like some reports of people's installs just running unusually high on cpu usage ). But if you can iron out those issues then it's no problem.
Linux can also normally get better battery life because it can truly spin down the hard disk almost completely where Windows can not and does not, along with some other issues like that.
My best advice ( although I'm on Arch most of the time and don't know Ubuntu's packages by heart, or whats installed by default ) is to make sure you have your disks spin down when not in use, display dimm when not in use and turn off a few minutes later ( basic dpms features ).
When I first got my Dell it's Windows install had estimated 6 hours of battery life ( factory estimate was 8 ), didn't keep Windows on it long than the first boot to grab a couple of files. My Arch installs get 8-9 hours of battery life ( with a 66% capacity as of now ) with no problem.