Battery Life on i7 13” playing back SD Video

Discussion in 'MacBook Air' started by tyronehowe, Sep 1, 2011.

  1. tyronehowe macrumors newbie

    Aug 8, 2011
    A few days ago I performed a simple battery test on my i7 13” 2011 MBA.

    Display was at 4 bars from full, WiFi on but unused, playback of SD movies at full screen. The battery had already been cycled twice.

    When I first unplugged the power lead and started video playback the battery monitor show 4h 49m remaining. This proved to be a pretty good approximation; the computer actually turned itself off after 4h 40m.

    I’m a bit disappointed with this. The processor remained at about 5%-7%, so it was hardly being used and yet my results are nowhere near the 7 hours that Apple advertises. I realise that the 7 hours can only be achieved with light usage – but I feel that playing back a simple, non-HD video file with processor usage of 5%-7% IS light usage. :confused:

    Anyone have a similar experience?

    Incidentally, I have an LG display - which I must say is a LOT different from my previous Samsung display, colours are noticeably less vibrant.
  2. impulse462 macrumors 68000


    Jun 3, 2009
    Did you watch in quicktime? Correct me if I'm wrong, isn't watching the video GPU accelerated?

    In that case, more of the GPU was being used and less of the CPU (hence the low CPU usage). Did you get a look at your CPU temperature while watching the video? Since the CPU and GPU are on the same die, that could give you an estimation to the GPU's temperature (due to proximity) and in turn the GPU usage. We can't know for sure, however.

    I find this weird because Thisismynext did a similar test and they got 6ish hours of battery life (I think). I'm not saying there is anything wrong with your battery, though. You may have to give the battery a few more cycles, but I doubt that you'll receive an increase in 1:20 hours of battery life.

    Anyone else have any thoughts?
  3. bill-p macrumors 68000

    Jul 23, 2011
    If you are really not using WIFI, definitely turn it off out right. Make sure Bluetooth and other such radios aren't running either.

    That should net you at least an extra 30 minutes.

    Then watch for cases, hot environment, etc... elements that may obstruct air flow and heat dissipation of the device as the battery drains much faster when it's heated up.

    If you are in a freezing room, your Macbook should net another 30 minutes of battery life.

    So doing both of those things should get battery life closer to "test lab" figures.
  4. tyronehowe thread starter macrumors newbie

    Aug 8, 2011

    Thanks for the replies.

    I was using VLC to playback the video. The temperature of the CPU goes up only slightly to 52/53 degrees.

    Yes I could turn WiFi and Bluetooth off, but I usually use both all the time, and I assume that Apple’s test at least included WiFi.

    The environment was standard office – normal temperature, MBA stood on a desk and not surrounded by clutter.

    I was never expecting to see 7 hours use for moderate to hard use, but I was hoping that playing back a video with just a few percent of CPU being used would be close.

    But even so, it’s a fantastic machine and I wouldn’t part with it for anything – well, not until the next MBA update anyway!
  5. iphonsteve4ajob macrumors regular

    Aug 6, 2011
    I guess that's why Apple doesn't specify "what" kind of light usage will get you close to the 7hr mark. If I turn off my radios, turn down keyboard to three bars, screen to four bars, and open my word processing app, I see the "battery time" indicator jump really high. Though I've never had the chance to test this on the road, it's kind of cool knowing that I could potentially get 8-9hrs of word processing time in. Now of course if I start Safari and do a bit of video watching I'm right back to 5-6hrs.
  6. bill-p macrumors 68000

    Jul 23, 2011
    Apple's test is actually an even lighter situation.

    They do keep WIFI up, but the CPU only kicks in at 15% briefly for less than 10 seconds every... 1-2 minutes or so. The computer most likely sits completely idle otherwise.

    Meanwhile, your test likely forces the CPU to constantly stay at 10% usage the entire time. That does make a difference.

    As an aside, I have a 2010 13" model, which I can squeeze 11 hours out of consistently surfing the web as described above, but only when not watching videos. HD videos get battery to show 3 hours at 99% mark, and SD only does slightly better at 4 hours, with brightness at 8 bars, or 50%. If that's any indication, I would say your test result is definitely normal.
  7. bursthead macrumors 6502


    Apr 9, 2010
    OP: I have a question... Did you happen to have Mail running? And if so, was it set to manual push or auto retrieve? What was your brightness and keyboard back light settings?
  8. jdechko macrumors 68040

    Jul 1, 2004
    How were the videos encoded? I know you said SD, but there is a big difference between AVI-DivX, mkv, mp4 baseline and mp4 H.264. Only the last one is GPU accelerated. It can make a pretty big difference.

    Also, there is something with CPU's known as rush to idle, where a CPU will finish as quickly as possible in order to power down 1 or both cores. So the 5-7% could have used more than you thought.

    Having said that, as other posters have mentioned, at nearly 5 hours, the battery life seems right about average for your usage.
  9. tyronehowe thread starter macrumors newbie

    Aug 8, 2011
    Thanks for the replies. :)

    @ iphonsteve4ajob: I can certainly remember regularly getting more than 7 hours battery on my 2010 MBA. Wifi off, but BT on, mixture of word processing, some video play, lots of iTunes music playing.

    As I said, I’m not expecting anything like 7 hours if I’m doing “serious” work – using Logic, viewing lots of flash web pages and so on. I was just hoping that sub-10% of an i7 CPU was considered as “light” usage. Clearly, I’m wrong!

    @bill-p: I think my battery life, as you say, is normal. I’m just a little surprised that (what seems to me) a trickle of CPU usage should leave me with 4.5 hours usage. Do I wish Apple had extra battery life by making the MBA heavier? Definitely not!

    @bursthead: Mail was not running, screen and keyboard were 4 bars from full, keyboard to auto turn off after 30s.


    @ jdechko: m4v files created by Handbrake in Universal mode from a DVD.

    Yup, seems my battery usage is what others expect. In that case, I’m happy. :D
  10. spacepower7 macrumors 68000

    May 6, 2004
    Try installing little snitch and see how often Mac OS and other apps use wifi without your knowledge. I'm looking at you Chrome, and many Apple and 3rd party apps.

    It's interesting to see the places your Mac connects to when you aren't paying attention. All of your ISP's dns servers talk to you Mac ever few minutes.

    I'm working in Florida this week and even when my Mail and web browsers are closed, my computer is pinging half the state, even hundreds of miles away. Thanks comcast ;)
  11. scarred macrumors 6502a

    Jul 24, 2011
    Almost 5 hours of battery life watching a movie... I guess it's all about expectations, but to me that is a good result based on what the Macbook Air 13 really is (a full fledged computer, with a decent size lcd).

    Certainly, it pales in comparison to the iPad, which frustrates me as well. I want the best of both worlds please! Give me cpu power when I need it, but fall back to something the sips electricity when I don't. Sandy Bridge is a great step in that direction, but still lots of room for improvement.

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