Hypothetical question... You are away from home and your 17" Unibody MBP is asleep at home, connected to the power supply. There is a power failure in your home area and when you get home there is still no power. So you want to use battery power for a few hours. But the battery has run down because it switched to battery when the power was cut. Is there a way to prevent the battery kicking in when power is cut in sleep mode, so that in such an emergency, the battery has not been run down by the time you get to want to use it?