This problem happened to me twice on 2 different OS. first in Snow Leopard then in Lion. My battery would be fully charged then when i would take it off the charger, the battery would jump from 100% to 6%. I know that i always keep my charger on whenever i'm using it and i calibrate at least once a month. i sometimes use about 30% of battery out of a 100% then i'd plug it back in the charger. does anyone got any idea on why it's doing that? is my battery defected? i have a MacBook Pro 13" Mid-2010 btw.