When I switched to Linux on my netbook I was surprised that the system was faster and going quite easy on resources, but the overall battery life was worse than on Windows.
There are great power enhancements and battery saving optimisations on Windows that Linux users could just dreamed about. But there is a tool from Thinkpad users that improves your battery life under Linux (and not just for Thinkpads!)
sudo add-apt-repository ppa:linrunner/tlp sudo apt-get update sudo apt-get install tlp tlp-rdw
The tool will run in the background and take care of everything else on your behalf.