I have a Macbook from early 2008, and right now it has 1GB of RAM (512 MB per bus). I was planning to switch from 1GB to 4GB, but I've heard that increasing the RAM significantly shortens the battery life. To what extent is this true? My battery is already pretty old, and doesn't last for more than 2.5 hours or so. Will switching to 4GB mean buying a new battery?