So Santa brought me a new Black MB for xMas and thus far I'm thrilled, still trying to get used to the keys though. Battery life seems spotty at best. Fully charged the battery time is only 2:20 and after only 15 minutes of use its down to 91% charge. Does the battery get better with charges? Should I be concerned? Seems like Apples claim of up to 6 hours is way out in left field.