displaymacmacbook promagsafe
When I connected MagSafe power cable to Mac and close lid, secondary display become a primary and dock migrate to it. But when I disconnected MagSafe power cable – the primary and secondary monitors both are turn off.
How can I set external display as primary and turn off internal display without connected MagSafe power cable?
I has Mac OS X 10.9.3
Under your System Preferences > Display, you've got this
Just drag the white bar to the other screen to set it as the main screen.
You might have to do that every time you reboot / reconnect the external screen.
Run sudo nvram boot-args=iog=0x0 and restart. It restores the behavior on 10.6 and earlier where the internal display is not turned back on if the lid is opened in clamshell mode.
You can delete the variable with sudo nvram -d boot-args.
Other related questions here and at Super User.
Best Answer
Unfortunately, according to the Apple support website, this is intended behavior. MacBooks do not support video output to external displays when running on battery power - you'll need to plug in the MagSafe cable.