There was a bit of controversy at the release of the 3.x kernel because it contained a power regression (or not a power regression but something else that behaved like a power regression depending on who was talking) and the result was that Linux got considerably less battery life than Windows on the same machines. This was especially obvious to dual-boot users. This is a long complex story, so if you’re interested in the details see the links at the end.
Whatever the state of your kernel, follow along to learn how to hunt down power hogs and tweak your system for best battery life with the latest release of PowerTOP.