I just purchased a 15" MBP matte, and it'll ship in a couple of days. I'm going to use it for work and home. I work 9-5. Should i charge it to full, and let it drain at work, or should it be plugged in all the time? I heard keeping a laptop plugged in full time kills the battery. Is this true? I'll be using the laptop everyday at work and a couple of hours at home. Recommendations for a long lasting battery?