when using an external monitor with a macbook pro (clamshell mode) does the macbook have to stay plugged in to AC in order for the monitor to maintain display? And if so, how does that affect the battery to remain healthy?

The short answer...

...yes, you have to keep the power adapter plugged in to use the external monitor.

If you're using your MacBook Pro with th external monitor and the computer plugged in, you needn't worry about the computer 'overcharging' - it won't and it can't. I use my MacBook Pro plugged into my Apple Thunderbolt Display 97% of the time. I have a reminder set every two weeks to disconnect from mains and let the battery run down to 30-40% and then plug it back up. My battery health is still at 99% even after using this method for well over a year now.

Clinton

Because closing the lid on battery power puts the Macbook to sleep (which this thread is all about) 🙂

Thanks - this helped me. Sometimes I need to unplug the power adapter for whatever reason (for e.g a co-worker needs it etc.). In that case, I open the lid and press Cmd+F1 so the screen gets mirrored on the external monitor. Good workaround and works for now.

I saw on another thread that Insomniax can turn off sleeping when lid is closed, meaning you can use clamshell mode without a power adapter: http://semaja2.net/ye-ol-projects/insomniaxinfo/ (the problem is that normally, with lid closed, removing the power adapter makes the computer sleep). I haven't used the software and can't vouch for it, but people on that thread seemed happy with it.

Hopefully, the OP had found the answer long ago - the question was asked 4 years ago.

And, personally, I would not download anything from anywhere but the app store unless I was familiar with the developer.

Hi NiqueXyZ -

There are two third-party applications that will allow you to create "Prevent computer from sleeping on full battery power when connected to external display" functionality. They are InsomniaX and Caffeine. I just installed InsomniaX and am now using my two external monitors with the Mac lid closed and no power cord plugged in. Hope this helps!

Hi inquiring1mind,

Here's some information I found concerning your two questions:

Mac notebooks: How to use your computer in closed clamshell (display closed) mode with an external display

http://support.apple.com/kb/HT3131

Requirements for closed display mode:

• Power adapter
• External keyboard, mouse, or trackpad
• External display

You can find more information about maintaining your battery's health here:

Apple - Batteries

http://www.apple.com/batteries/

Cheers!

- Ari

You're welcome!

Clinton

Absolutely, I am glad it helped!

Have a good one!

- Ari

Is there a workaround for this? I no doubt want to keep my Macbook hooked up to power while using an external display but sometimes I accedentally unplug the power cord. Its easily done seeing that the cord is only held on by a magnet. I hook it up with the cable running up the side of my desk so i can easily stash it away and take it and my Mac with me.

Apple's list of requirements ("Power Adapter") is unfortunately very clear, until I saw that I was hoping it was a bug that will get ironed out at some point, especially since I got the weird feeling it wasn't always like this.

Anyway, my workaround is to leave the notebook display just slightly open, perhaps 1-2cm before the Macbook takes full clamshell position. This will keep the Macbook's own display active and the computer running. To save a little battery power, I tune down the brightness of the internal display to an absolute minimum, using the internal keyboard of the Macbook (using the external keyboard's brightness keys changes the brightness on the external Thunderbolt display).

Hope this helps someone.

Why don't you just close the lid?

Use these steps to enable closed clamshell (display closed) mode:If you are using a wired keyboard and mouse:

1. Make sure the computer is plugged in to an outlet using the AC power adapter.
2. Connect a USB keyboard and mouse to your computer.
3. With the computer turned on connect the Mac notebook (using the appropriate Apple adapter if necessary) to the appropriate port on the external display or projector and turn the display or projector on.
4. After your computer's Desktop appears on the external display, close the computer's lid.
5. When you close the lid:
   • In OS X Lion and later, the external display will change to a blue screen, then will show your desktop.
   • In Mac OS X v10.6.8 and earlier, wake the computer up by clicking the mouse button or by pressing a key on your external keyboard.

You should now be able to use your Mac notebook as you normally would, with a USB keyboard and mouse.If you are using a Bluetooth keyboard and mouse on a Bluetooth enabled Mac notebook:

1. Make sure the computer is plugged in to an outlet using the AC power adapter.
2. Verify that Bluetooth is turned on by using the Bluetooth pane of System Preferences or the Bluetooth menu icon.
3. Pair your Bluetooth keyboard or mouse with the computer. For step-by-step instructions, see this article forkeyboard pairing or see this article for mouse pairing.
4. In System Preferences, be sure that the Allow Bluetooth devices to wake this computer option is selected.
5. With the computer turned on connect the Mac notebook (using the appropriate Apple adapter if necessary) to the appropriate port on the external display or projector and turn the display or projector on.
6. After your computer's Desktop appears on the external display, close the computer's lid.
7. When you close the lid:
   • In OS X Lion and later, the external display will change to a blue screen, then will show your desktop.
   • In Mac OS X v10.6.8 and earlier, wake the computer up by clicking the mouse button or by pressing a key on your external keyboard.

You should now be able to use your Mac notebook as you normally would, with a USB keyboard and mouse.

Read the post above yours before digging a bigger hole for. You can operate the Mac with the lid closed and an external keyboard and mouse.

In short, you are wrong.

OOpps

Only on AC power, you're correct about when on battery power.