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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  • Esko747 - Thursday, July 04, 2013 - link

    Thought: Would using an efficient laptop cooler increase the performance at noticeable rate? The chassis in these are after all used as a heatsink, and the main thing stopping the processor from using higher clocks for longer periods of time is heat. Reply
  • IntelUser2000 - Thursday, July 04, 2013 - link

    That depends on whether cooling solution in the Macbook Air is good enough for the TDP or not.

    Yes, if the system is substandard, minor to zero if its not. Haswell uses similar Turbo system to Sandy/Ivy Bridge where it has a "guaranteed" Turbo and higher "opportunistic" Turbo, which the latter would turn off after a certain period regardless of how cool its running(to keep it at 15W power use averaged out over longer periods).

    I'm guessing the 2.8GHz reached for the Core i7 in the Multi-threaded suite is the "opportunistic" Turbo, and in infinite time periods with sufficient cooling, it'll settle at 2.4-2.5GHz.
    Reply
  • SteveKen - Monday, July 08, 2013 - link

    Love my job, since I've been bringing in $82h… I sit at home, music playing while I work in front of my new iMac that I got now that I'm making it online. (Home more information)
    http://goo.gl/FdFf2
    Reply
  • FwFred - Thursday, July 04, 2013 - link

    This reminds me of the Nexus 4 freezer test. Anyone willing to stick their MBA in a freezer??? All in the name of science of course. Reply
  • mavere - Thursday, July 04, 2013 - link

    Based on my past experience, the Macbooks don't thermal throttle until ~100C, so within the context of this article, I doubt there'd be much difference.

    That might change with the fan gets dusty, though. One can also reapply the thermal paste inside the machine for a (frustratingly) consistent 10-15C drop and lower fan noise.
    Reply
  • dsumanik - Thursday, July 04, 2013 - link

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

    -anand lai shimpi

    Direct acknowledgement the initial 2013 air review left you with a sense of disappointment, and sub par performance. Yet you read that review and its all roses, praises and recommendations, furthermore followed by a direct advertising "best mac laptops - June 2013" article, which recommends purchasing the same laptop.

    I mean after all if the 2013 MBA was so great there would be nothing to "fix"

    RIGHT?

    RIIIIIGHT?????

    Samsung made a new PCIE SSD and intel released a new processor.
    Apple put it in the same package. That is ZERO ZERO ZERO innovation.
    They are still recycling products from the JOBS ERA thats why the stock is going to continue to fall.

    You want them to start innovating again Anand?

    Rip apple a new asshole when they re-release this same junk!!!!

    I have been coming to this site for over a decade.

    You, anand, personally, directly, have lost your impartial journalism and professionalism.

    is Tim Stevens on your speed dial or what?

    What possible motive could you have for ignoring the facts and promoting their products blindly like this?

    There is only one explanation......like many other media blogs, AT has substantially invested and now lost money in apple stock, or are directly, or indirectly getting kickbacks and are now trying to stop the bleeding.

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

    EXCEPT

    - same design as last year- stethoscope when plugged in, switch the TB PORT!!! NO BRAINER!!!

    - in 2013 a "premium apple experience" delivers 1366 x 768 resolution.. I mean come on 1998 era 1600x1200 would have been at least SOMETHING LOL..and absolutely technologically possible.
    I mean come on you have double the battery life now!!!!!!!

    - no 16gb ram option???? so cheap and easy to do. But nah, peeps will still buy it. Thaty is exactly how the board meeting on that one went.

    - no LTE or modem support, you should buy an iPhone for that.

    - there are wifi problems galore with the new model, and wifi limitations within OSX itself....don't believe me? .... you reported it in your last article but any MBA owners running boot camp have known this for over a year now....you need to transfer a big file? Boot into windows and cut the time in EXACTLY half.

    Eff this shit im out, this site's owner is straight up corrupt...at least he got burned on apple stock for it.

    Pay backs a bitch huh.
    Reply
  • JKflipflop98 - Thursday, July 04, 2013 - link

    People like you are a cancer on this Earth. I hope you finally succumb to your syphilis infection. Good day, sir. Reply
  • KoolAidMan1 - Friday, July 05, 2013 - link

    Apple haters are more annoying and idiotic than any Apple fanboy, which is quite an achievement. People like this are amazing Reply
  • iwod - Friday, July 05, 2013 - link

    Yes, Apple Fanboy and Haters, the irony. The truth is, Anyone, absolutely anyone who work within the industry would have had at least a little bit of respect to Apple. Be it Intel, AMD, or heck even Samsung or Google. And by ALL standards Apple has consistently put fourth one of the best hardware.
    So in that sense Apple Fanboy are at least better, because even if they know jack about Apple it still have a product that is worth talking about.
    And Apple haters, are like you said annoying as hell as most of the time they dont have a clue about what innovation actually means and literally knows nothing about design, engineering and tech. And what's even worst is that they "think" they know a lot. And They just hate because they hate.
    And back to those work within the industry and why they actually have a little respect for Apple? Because they actually know their stuff. Not just clueless mind bogging trolls who goes on the internet everyday reading mostly incorrect and false statement and pretend they know a lot.
    Reply
  • dsumanik - Friday, July 05, 2013 - link

    nothing to do with apple love or hate...I've pointed out that anand wrote a positive article about the MBA, then in his own words, revealed deep down inside he felt it needed "fixing"

    He then went on to write a second article further promoting this product, specifically promoting it.

    Connect the dots folks, stop changing the subject to apple vs microsoft and goole, i know your hamster brains are trained to do that...its reflex now....but my point was ananda bias, and then advertising of a product he was surprised to find slow, and at best on par with last years model... and still unchanged as a platform and product as a whole.

    dont hate me cuz it has an apple logo on it.
    Reply

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