Programs can also be guilty of sucking up the power.
How can you find out which ones?
With Activity Monitor. It comes with Mac and can tell you everything you need to know about the applications running.
Activity Monitor says how much CPU, RAM and Virtual Memory your applications are using and more. You can use it to see which programs are slowing things down.
Checking activity monitor every once and a while can give you insight into which applications are holding back your computer.