Hi all - I have a mid-2007 model 15" macbook pro purchased in August 2007. Lately I have been getting about 15 minutes of battery life when not plugged in. It will say like 80% and 1 hr 30 min remaining but then all of the sudden my computer will just shut off. Also when plugged in now it says the battery is not charging but it will show levels as low as 41%. Is this a common problem? What do I need to do to fix these issues? Thanks so much!