Hello, My arrandale mbp battery is running very well, what seems to be off is the % / time remaining. For example, when it was at 100% battery it said "4 hours remaining". I've been using it for about 4 hours and I'm now down to 40%. Now, at 40%, it says 1.5 hours left but I really doubt that's accurate. How can I calibrate? Since I got this mbp, I have not let battery reach 0. Should I do that?