I bought my MBA a couple of days ago and out of the box it had about 80% battery. I've not had to charge it yet as I've only been using it lightly... eg. just playing around and getting to grips with my first Mac. It's now down to about 18%. Shall I wait until it gets to near 0% before charging or charge it now? I read somewhere that after it's fully charged you should leave it plugged in for 2 hours. Is this still true? Also, is it better to leave the MBA plugged to the mains when possible, or run it on battery?