My new 17" powerbook is only getting 2 hours off a full battery charge. Is that normal? Also, I think I read somewhere you're supposed to let the battery drain to 0% once so it can fully charge. However, the computer automatically sleeps when it runs low on power and never actually gets to 0. When I hit the little button on the battery one green light is always on, no matter how low the power. Any thoughts? Thanks in advance.