Hey all. Bought this 13" MacBook back in September 2006. Recently have started using it a lot more "out and about" and have noticed a significant change in my iStat's battery readings. While it was regularly (for the battery health reading) around 90%, it now fluctuates between 60 and 75%. What have I done to hurt the battery this much? Is this something that would be covered by AppleCare? Suggestions for maintaining the battery better?