Those who care about the life-time of their battery would not leave their laptop battery over-charged. They usually take it out, when the laptop is connected to the power supply the whole day. That makes a lot of difference after a few years. With the non-replaceable battery, one wonders if there is a proper circuitry to prevent over charging the battery. Apple battery care: http://www.apple.com/batteries/notebooks.html "Apple does not recommend leaving your portable plugged in all the time."