Hi! My father has an older MBP hooked on an external display. After upgrading to Mavericks, he said his external monitor would turn off when running on battery, a behavior which was not present on previous OS. I tried googling but found no solution. He lives in another city so I couldn't try to troubleshoot it myself. Any idea? Also, his computer is very sluggish on 10.9. I suggested repairing the permission, as suggested on the Internet. It fixed it briefly but the problem returned. He did it again but this time it didn't help. Any idea?