Recently my battery keeps dying much quicker than it used to. When there's around 20%-30% charge left it will usually shut down now. I'm not sure what to do at this point. It's health at the moment is at 56% and has a total of 28 cycles. Do I have a defective battery? I bought the Macbook Pro back in July of 07 so I'm sure the warranty is still intact. What should I do? PS: Yes I have been calibrating my battery at least once a month.