One of the biggest problems I have had with my three-year-old PowerBook is that the battery no longer lasts as long as it used to. When I first got it, I could easily get three hours of use out of it. Now, I'm lucky if I can get 30 minutes. It turns out that Lithium-Ion batteries only have a 2-3 year lifetime. I decided to buy a new battery, which has a slightly higher capacity than my original battery. It was well worth it: My PowerBook is back to its old battery life. I also learned that the life of Lithium-Ion batteries can be extended by keeping them at 40% charge and near 0° C. I am definitely going to be doing that with my new battery to see how well it works.