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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

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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.

  • Alternatively you could use third party software like Caffine to prevent the machine from sleeping when you close the lid, doing so however will not turn off the primary monitor when you close the lid and so will not automatically move your dock either. – Fyrefly Jun 30 '14 at 15:09

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