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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  • KoolAidMan1 - Sunday, July 07, 2013 - link

    Your post is filled with angry rhetoric. It is hard to take any of that seriously Reply
  • asianwolf - Sunday, July 07, 2013 - link

    what an amazing amount of drivel from a single post. Let's look at the one word you have used against this product 'innovation'. Prey tell please any other manufacturer in this sector that has 'innovated' in any way using the same standard Intel/hardware components?

    I'm not saying that Apple have 'innovated' in any particular way in this product as opposed to the original MBA introduction, this is just another internal upgrade...like all of the followers around them.

    Back up your thoughts with what you expect to see, rather than deriding a product that still excels amongst many of it's peers...not perfect...but neither are the components that its built from.
    Reply
  • therodt - Thursday, July 18, 2013 - link

    Guys he is completely right. Its not innovating if it is not new. Refining the same thing and calling it new does it make it innovative. Reply
  • pav1 - Sunday, January 19, 2014 - link

    The trouble is there is a conflict between innovation & pricing/value. Innovation is costly, and may not be included for low end products. You'll find innovation at the low end only for competitive reasons. Apple has significant mind and marketshare. Reply
  • whosjohnny - Monday, September 23, 2013 - link

    dsumanik - you're a cancer, stfu man. you know NOTHING about innovation. something as good as macbook air single body design and you're like what? "release this same junk!!!" go f die you imbecile! Reply
  • hasten - Thursday, July 11, 2013 - link

    Unfortunately everything you have written is wrong. You are the problem - fanboys that believe anything they read on the internet. Apple has not "innovated" since the early 90s. They have done nothing but taken someone else's innovation and repackaged it in a well marketed shiny box. Claiming that they have "put fourth" the best hardware shows even more how little you know. Apple does not manufacture anything. They depend on true hardware companies to create for them. Yes they do assist in the design of the mobile, low end processors for their mass market products, but they do not manufacture anything.

    Amazingly the shroud is coming off and investors and the general public alike are realizing the game that Apple has been playing. Stock prices plummeting, market share decreasing. I'm sure that hard statistical facts won't mean anything to you though. I'm sure you work in the industry with your commentary, brilliance is spewing from them. The only people that should have respect for Apple are marketers. The bubble is bursting and the kiddies are sad.
    Reply
  • purerice - Friday, July 05, 2013 - link

    JKflipflop98, while I do not wish harm on anybody, I share your disgust with dsumanik.
    I have no inclination of getting an Apple MBA but Anandtech's MBA articles are great for comparing IVB to Haswell and i5 to i7, at least in a GPU-limited scenario.
    I am in the market for a new laptop and often see great deals on IVBs and the i7s are extremely tempting. However thanks to Anand's articles, I will wait for the full Haswell line of i3, i5, i7s to be out before deciding.
    Also, considering the meager difference between i5 and 30% higher clocked i7, unless it is to do with thermal limits, I think I will stick with an i3 or i5 based Haswell. Though I would be curious in performance difference between these 15W i7s and the 47W i7s in Toshiba's laptops in performance, battery life, and temperature.
    So yes, even if I now have no inclination of getting an Apple MBA, these 3 articles provided enough information to deduce what processor I want in a laptop. As laptop processors are not generally interchangeable, these articles have helped me to key in on which laptops to eliminate from my search. To that extent I am very grateful to Anandtech for these articles.

    Furthermore, even if you don't like Apple, Apple generally has consistent hardware from generation to generation and often gets early editions of Intel processors (great for getting rid of deep sleep USB3.0 issues). Thus, with fewer variables from generation to generation, Apple computers make great test beds for testing out those few variables which are new. It is both amazing and sad that on a website with "tech" in its name you get people who think as unscientifically and biased as dsumanik that they cannot appreciate genuine research for the name behind the research.

    Good day to you all and thank you Anand for your continued dedication to solid articles that give insight that is valuable even to those will not likely purchase the product reviewed. I salute you.
    Reply
  • dsumanik - Friday, July 05, 2013 - link

    Stop turning the conversations towards apple vs whoever. My rant has nothing to do with apple being good or bad.

    Its ok for anand, you, me, or the rest of the general public to like apple.

    it's NOT ok for him to tell you apple is good when he isnt thinking that inside his own head.

    Why why... WHY would you ever tell someone to buy something you thought was inferior?

    "Oh man, the Core i7 upgraded seriously fixes everything."

    Ok so anand was thinking it was broken. Ok maybe not broken, but at the very least slow...a step down from last years performance. its plain to see in the numbers, the new proc isnt a flat win across the board.

    Yet he still gave the original MBA a glowing review....then wrote a separate article recommending its purchase. Like that was the icing....why did he write that article lol? wouldn't you write that after apple had refreshed its entire line?

    Why right now...all of a sudden do we need an article telling us to buy the only 2013 model.....no one here is stupid, we know not to buy the last years model of anything!!!!!

    its so LOL wtf obvious if you just take a step back and ask why, especially that second "article", why it was written.....*advertising* cough cough cough

    his true feelings were NOT reflected in the original article. End of story.

    he WANTS apple to be viewed in a positive light, even if he isn't feeling it inside himself.

    This isn't an isolated incident its been slowly happening for about 3-4 years now.

    He is writing articles telling you to buy something, that in his mind he felt was subpar.

    like seriously guys, don't you see a problem with that?

    ask yourself why someone would make that recommendation?

    Hate me all you want but the question still needs answering....why is it of PERSONAL interest for him to paint apple as rosey a picture as possible.

    It has nothing to do with me, my attitude, my love or hate of apple, Microsoft, chocolate, vanilla, titty bars, democrats, gun laws, religion, or the color of your skin.
    Reply
  • biasuz - Friday, July 05, 2013 - link

    I'm sorry sir, but your premise is false.

    I know nothing about Anand besides what's resides inside this website. That accompanied to a review of intel's pentium IV a real while ago turned me into a regular visitor.

    On both of the very well written articles relating this subject matter, Anand has been clear to accurately explain the DESIGN CHOICES Apple took, when building a computer whose main focus is not a performance crowd.

    Such design choices are:
    - use of slower frequency CPU would for sure impact raw processing power, as has been perceived by the reviewer, who in fact went to the trouble of quantifying how much less raw power would you get when comparing a previous model. Now please, kindly take into consideration what sort of gains in term of battery life were achieved, WITH LITTLE TO NO IMPACT in consumer experience, because of such DESIGN CHOICES.

    - The same philosophy can also be observed in using a lesser frequency in a MUCH LARGER GPU, demoed similar to superior performance with noticeable gains in used wattage.

    This computer is all about mobility, no raw power.
    In it's premise of existing, a mobile computer, this ones generation seriously outperforms it's previous generation.

    Kind regards.
    Reply
  • vFunct - Saturday, July 06, 2013 - link

    lol.

    You DO know that Apple makes the best computers in the industry, and everything else is largely garbage, right?

    THAT is objective fact. Do not attempt to spin it with your bias.
    Reply

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