Battery Life

I ran the i7-4650U based 13-inch MBA through the same suite of battery life tests as the un-upgraded base model. What's important to note about all of these tests is that the amount of work done per cycle of the test doesn't vary based on performance. There's enough idle time baked in to make sure that the Core i7 based 13-inch MBA isn't artifically penalized by having to do more work than the i5 model simply because it's faster. The other thing I noticed while testing these two machines is that although both were equipped with the exact same Samsung panel, their brightness curves were slightly different. At the same brightness setting under OS X (or Windows 8), both panels responded differently. Both were capable of similar max brightness values but it's clear that either Apple is doing some calibration here that's panel lot specific or there's a significant variance in how these panel/backlight/electronics combinations respond (or both).

I reproduced the battery life test details below:

The light and medium suites are inherently related - they use the same workload and simply vary the aggressiveness of that workload. The light test hits four different websites every minute, pausing for nearly the entire time to simulate reading time. Flash is enabled and present on three of the sites. The long pause time between page loads is what really makes this a light test. Web browsing may be the medium for the test but if all you’re doing is typing, watching Twitter update and maybe lazily doing some other content consumption this is a good representation of the battery life you’ll see. It’s a great way of estimating battery life if you’re going to be using your notebook as a glorified typewriter (likely a conservative estimate for that usage model).

The medium test hits the same webpages (Flash and all) but far more aggressively. Here there’s less than 10 seconds of reading time before going onto the next page. It sounds like a small change but the impact on battery life is tremendous.

Both the light and medium tests are run in their default state with processor graphics enabled, as well as with the discrete GPU forced on. I run with the dGPU on as well because it’s far too often that a single application open in the background will fire up the dGPU and contribute to draining your battery. The goal here is to deliver useful numbers after all.

The final test is very similar to our old heavy multitasking battery life tests, but with some updates. Here I’m downloading large files at a constant 1MB/s from a dedicated server, while playing back a looped 1080p H.264 movie (the Skyfall trailer) all while running the medium battery life test. The end result is a workload that gives you a good idea of what a heavy multitasking usage model will do in terms of battery life. I’ve found that OS X tends to fire up the dGPU anyway while running this workload so I saw no reason to run a separate set of numbers for processor and discrete graphics.

Light Workload Battery Life

In our mostly idle workload, there's virtually no difference between the two parts in terms of battery life. The i7-4650U is actually able to boast a slightly higher number here but for all intents and purposes the two are equal. Apple's 12 hour estimate comes from a slightly lighter workload than what we run, so I see no reason that Apple couldn't claim equivalent max battery life regardless of what CPU option you pick.

Medium Workload Battery Life

Under load we begin to see the expected: the Core i7 upgrade does have a power cost associated with it. There's around a 13% reduction in battery life here compared to the standard 13-inch MBA configuration. Heavier workloads tend to force the CPU cores into higher frequency (and thus higher voltage) states. In the case of the i7 both the frequency and voltages are higher, which drives power consumption higher than the i5 resulting in lower battery life.

Heavy Workload Battery Life

The gap between the i5 and i7 grows to its largest point in our heaviest workload, which makes sense. Here there's around an 18% reduction, or almost a full hour of battery life (52 minutes). If you ran both processors at full tilt nonstop (think looped Cinebench until both batteries die) you'd probably see an even larger gap. In this case I think the differences here are pretty reasonable expectations for most target usage models of the MacBook Air.

Thermals

As the MacBook Air isn't a handheld tablet, the limit for what's an acceptable max skin temperature is much higher. Just as there's an impact on battery life with the Core i7, there's also an impact on thermals. I ran a CPU and GPU intensive workload and measured thermals at three different points on the system: max temperature on the keyboard side of the system (upper left corner of the keyboard), max temperature on the bottom of the machine as well as the max temp reported by the CPU core proximity thermistor.

13-inch MacBook Air (Mid 2013) CPU Comparison - Observed Temperatures
Location Keyboard/Top Bottom (sustained) Bottom (max) Internal CPU Proximity Thermistor
Intel Core i5-4250U 47.1 °C 41.4 °C 41.4 °C 92.2 °C
Intel Core i7-4650U 47.7 °C 42.1 °C 46.6 °C 96.7 °C

Average temperatures aren't substantially higher on the i7, however you will notice that there's a column for max observed temperature on the bottom of the chassis where the upgraded MacBook Air does show a considerably higher temperature. The higher temp isn't sustained but I did record occasional blips up to 46.6 °C on the bottom of the chassis while the i5 model pretty much topped out at its sustained temperature. Internal temps are obviously much higher as well.

The impact on acoustics wasn't really noticeable. Under extended load both systems hit the same 6500 RPM fan speed, which given the same cooling system produced identical acoustic profiles. I tried to see if the i7 would ramp to 6500 RPM any quicker than the i5 but in most cases I don't believe it did, at least appreciably so.

Core i7 vs. Core i5: Understanding the Power Story Final Words
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  • GotThumbs - Monday, July 08, 2013 - link

    @dsumanik: I feel your frustration and can see what your point is about. I've actually been coming to AnandTech since Anand was in HighSchool. I also have been disappointed in what I perceive as "Marketing spin" type reviews.
    Other than swapping in an updated CPU's and SSD's, what's the REAL effort/innovation for the 2013 line? Not much, but yet how many articles have been written and what is the overall feeling of each of those "reviews"?
    I've gotten to the point where I actually find it funny/amusing that so much "pomp and circumstance" has been put into recent Apple articles. When people ask me why I don't have an Iproduct, they are totally amazed when I tell them I'd never want an IProduct. I understand it goes against the common thinkers, but I'm not a follower and I choose to avoid systems where I'm not in contol. It's my choice and I respect others decision to chose what they want.

    As far at Anand's recent "Reviews", (no disrespect to Anand as an individual), but It's like a car salesman spinning the minor differences between the new years models and last years. "Less powerful engine, but hey you don't really need/want that"

    At the end of the day, everyone has their own choice to make and while I'll never own an Apple product, its due to the overpriced and closed ecosystem Apple's created. When you're (Apple) pushing a cult like community...they (Fanbois) willingly follow blindly IMO.

    You can try to explain your point forever.....but you must realize they will never even consider your point. It' would be akin to treason for them to even acknowledge your point of view.

    Best wishes to all and enjoy your choices,
    Reply
  • amdwilliam1985 - Monday, July 08, 2013 - link

    "...I choose to avoid systems where I'm not in contol."

    Kind of wish I've read your comment 2 years earlier. I've got the 2011 13" MBA, although the overall machine feels good, somehow I can never shake the feeling that it's Steve J's labtop and I'm not "in control" of it. I use my MBA as a glorifying web browsing machine and for everything else, I go to my windows 7 machine :)
    For the same reason(iTunes), I've dumped my beloved 3gs for Galaxy S2 and S3.
    I'm probably one of the few control freaks who needs to know that I'm in control of my pc/phone, instead of someone else.
    Reply
  • TheinsanegamerN - Thursday, July 04, 2013 - link

    two things. A. 1366x768 if just fine for a 11 inch screen. 1440x900 is great for a 13 inch screen, and i wish more oems would use 16:10 screens.
    B. why would apple change a design that works? getting 12 hours of battery life, or close too it, is downright amazing for a machine this size. although, id love to see what would happen if they took current tech and put it in an older design mac, the battery life would be epic. soo much battery.
    Reply
  • Spoony - Tuesday, July 09, 2013 - link

    No, those resolutions are not fine. Of course people want 2880x1800 on their 13" notebook. Of course they want 2560x1600 on their 11" notebook. However, the MBA is an ultra-mobile platform meaning battery life and size take priority over other traits. High DPI displays have a considerable power cost, and apparently Apple felt that trading off display resolution for battery life was the right call in this situation. At some point you just can't beat physics and you have to compromise.

    If you don't agree, don't buy their product. I'm not sure I agree, so I bought something else.
    Reply
  • kleos44 - Friday, July 12, 2013 - link

    I am tired of hearing this argument. Throwing out statements like "you just can't beat physics" is wrong. Educate yourself on the physics of IGZO displays. Significantly higher resolutions AND LESS power draw than traditional display technologies. Every high end laptop is going to use them this year including pretty much every other Apple product. Reply
  • TheeGooch - Thursday, November 28, 2013 - link

    Well said. I've slowly went from anti-Apple to being a fan over the last 7 years. 2014 will be when I buy my first Apple computer because the stability, quality, and ecosystem that comes with Apple products. The design choices they make to balance price, functionality, and quality just jive with my own idea of how those should be balanced. It's weird to think back to when I hated all things Apple on principle. Once I got my 1st Apple product( the ipod) , that began to change. Reply
  • ESC2000 - Monday, August 12, 2013 - link

    It is not fine when it is on a $1,000+ computer. That is a premium price, and the display, with its low resolution and TN panel, belongs on a low end machine. Apple always does this: either the device is way overpriced or some feature is skimped on.

    There is no reason that this machine, with its poor display and processing sometimes shower than last year's version, should cost as much or more than a similar windows machine even though apple does not have to pay for a software license. All that money is just going to apple's bottom line. I never understand when prior brag about how apple is the most profitable: all that means is you are being overcharged.
    Reply
  • zh.aung - Friday, July 05, 2013 - link

    If you hate apples, go and eat oranges. Don't waste your time writing this junk. Reply
  • KoolAidMan1 - Friday, July 05, 2013 - link

    Haha, how much angry spittle is on your monitor right now?

    Funniest post I've read in a LONG time, thanks for the laughs
    Reply
  • robco - Friday, July 05, 2013 - link

    If you're going to say pay back's a bitch, note the apostrophe. It is a contraction for payback is a bitch. Nobody will take you seriously if you can't even write a coherent sentence.

    As noted in the review, performance is on par with the previous generation, but with substantially better battery life. For many users, this is a huge bonus. For those wanting more performance, the i7 upgrade is reasonable, and will not adversely impact battery life to a great degree.

    Apple's design has been copied, unsuccessfully, by several other manufacturers. The MBA remains one of the few ultrabooks to have a decent display, keyboard, and touchpad.

    Plenty of other ultrabooks lack a celluar modem. There isn't a lot of free space.

    The CEO of Apple is Tim Cook. Do a little research.

    The next version of OS X, which purchasers of the MBA will receive gratis, may in fact fix some of the issues. Of course, you could look at the review of the Razer Blade, a new gaming Windows laptop that comes with neither 802.11ac or the ability to add gig-E, something the MBA can do by virtue of its (correctly leaving out the apostrophe here as it's possessive and not a contraction) Thunderbolt port.

    So yes, the fact remains that the MBA has great battery life, fast networking, a good (admittedly not great) display, solid keyboard, and great touchpad. OS X continues to provide far superior battery life than Windows. If you must pollute the internet with this sort of screed, learn to write properly and do you research.
    Reply

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