Using MBP with external monitor while running on battery

Discussion in 'MacBook Pro' started by rhimbo, Aug 14, 2016.

  1. rhimbo macrumors member

    rhimbo

    Joined:
    Jun 21, 2009
    #1
    Hi folks,

    MBP 17-inch, Early 2008, 2.5 GHz Intel Core 2 Duo
    ASUS PB278 display, 27-inch, 2560x1440, NVIDIA GeForce 8600M GT

    I have an older MBP that I use with my external monitor most of the time. Unfortunately, I have to use AC power in order to use the external monitor. The MBP will not drive the monitor on battery.

    Could anyone tell me if the newer MBPs can operate an external monitor off of battery power? And, if so, which brand monitors? Need the monitor be an Apple monitor?

    This constraint has been very frustrating and disappointing. I'm working all day, and the battery remains plugged in all day. It has shortened the life of 3 batteries that I've had to replace since getting the external monitor. Prior to that I just used the laptop screen and my battery lasted for over 5 years!!

    Many thanks in advance....
     
  2. gim macrumors 6502

    gim

    Joined:
    Jul 27, 2014
    #2
    My MBP can definitely operate an external display (tested it with 2 TVs and a projector via HDMI so far) while being on battery power.
     
  3. rhimbo thread starter macrumors member

    rhimbo

    Joined:
    Jun 21, 2009
    #3
    Thank you, gim. Perhaps I'll let this battery go until it dies and then upgrade to a new MBP. Mine is showing some age in regards to performance...
    :)
     
  4. gim, Aug 14, 2016
    Last edited: Aug 14, 2016

    gim macrumors 6502

    gim

    Joined:
    Jul 27, 2014
    #4
    But are you sure that this is a normal limitation of the older models? Surely seems a little strange, why shouldn't it work on battery power? It could be software/driver related, maybe the graphics card is in energy-saving mode when your MacBook isn't plugged in?

    Edit: Found this answer on the Apple support forums, it's from 2008, so probably related to the older MBPs like yours.
    "Apple notebooks will drive a second display from battery power, but only when the primary display is also active, meaning for sure the lid has to be up on the notebook. I am not sure why Apple has chosen to architect things this way, but it's been like that for several generations of product by now.

    So if you don't mind leaving your internal screen running, you can do what you want, although the lid will have to be up at least a little bit. You can also dim the notebook screen to black out if you prefer."

    To be honest, I never close my MacBook while it's connected to an external display. I just dim the primary screen until it's off. It definitely works this way with the newer models.
     
  5. rhimbo thread starter macrumors member

    rhimbo

    Joined:
    Jun 21, 2009
    #5
    I realize now that my explanation was a little ambiguous. Yes, I meant to ask whether the limitation was limited to the older models. And, when I first started this thread I wondered whether the situation was different if using an Apple monitor.

    OK... I just tried raising my lid and now I can operate on battery to drive both the primary display (laptop screen) and my external 27" ASUS monitor.

    The problem, however, now is that I am losing resolution on the ASUS monitor. The resolution on the primary screen seems to remain unchanged, but the external monitor is now in a vastly diminished resolution. I only have 512 MB of video memory which appears to be shared.

    I imagine the newer models can drive two displays of much higher resolution.

    Thanks for the information...!
     
  6. Samuelsan2001 macrumors 603

    Joined:
    Oct 24, 2013
    #6
    Yeah you can't use clamshell mode on battery that's an OS limitation.
     
  7. gim macrumors 6502

    gim

    Joined:
    Jul 27, 2014
    #7
    It was a little misleading because you didn't mention that you want to use it in clamshell mode ;D

    Can't you change the resolution in the system preferences under "Displays"? In the standard setting, your desktop is mirrored on the external display, which is why the highest resolution, that's supported by both displays, is automatically chosen.
    When I plug in my TV, my internal rMBP screen turns the resolution down to 1080p for example, because that's the maximum my TV can display. It's the other way around for you, because your external monitor has a much higher resolution than the internal one. But you should be able to change it in the settings..
     
  8. rhimbo thread starter macrumors member

    rhimbo

    Joined:
    Jun 21, 2009
    #8
    I've attached a screen grab of my "Display" settings. My external monitor is already at the highest resolution. Did I understand you correctly... you suggested I increase the resolution of the external monitor?
     

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