Hi,
Enough small talk, I remember reading about this in the manual for my 12".
It's called calibrating the battery, every time you get a new battery or 'book, charge it without turning the book on, when the battery is finished charging, disconnect the book from the power, then turn it on. Run the book until the battery is so low that the book shuts itself down, then plug the book back in to charge the battery. When the battery is done charging, the battery has been calibrated. I'm not sure how this applies to MacBooks, but if you have tried everything else, this did work for me. Tell me if it helps.
-Jess