I have a MacBook Pro C2D 2,33 GHz, 2 GB. It is one of the first models after the transition to C2D. Until now I did not have any problem with it. But last week suddenly my battery's health dropped from 93% to 33%. I tried to calibrate the battery but it did not work. Sometimes my battery health jumbs to 93% and after back to 35%. Do I need to replace my battery?