After about a month of having my MacBook, 50% battery capacity is only 1 hour 30 minutes, instead of the 2 hours that it was when I first got it. Is this drop in capacity normal?! Or is it fixable by recalibrating the battery? Also, is it a bad idea to leave my MacBook plugged in? Does the computer stop charging at 100% or does it continue? I thought that behavior was only found on older computers.