Can I run my MacBook in clamshell mode without being connected to power?

"This page suggests a workaround:


Set the display mode to mirroring (use the F7 button).
If you haven't done so already, attach the external screen, keyboard
and mouse.
Press a key on the keyboard (like Shift) and click the mouse once.
Close the lid and wait for the Macbook to go to sleep.
While sleeping, click the external mouse once, the Macbook will
wake up.


If all goes well, the external screen
will display the Dock and menu-bar
after a few seconds. As soon as you
see this, the Apple logo on the
Macbook shouldn't light up, open the
lid of the Macbook. The Macbook won't
go to sleep, won't power up its
built-in screen and you can now use
clamshell mode in lid-open mode.

EDIT: See comments on this post for kch's experiences with this method."

"In 2020, I believe Amphetamine app is the best way to achieve that.
I was able to create a trigger based on whether external monitor is plugged or not and battery level. Awesome!
apps.apple.com/app/amphetamine/id937984704?mt=12
My trigger setup"