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
POST A COMMENT

127 Comments

View All Comments

  • lilo777 - Saturday, July 06, 2013 - link

    MBA will soon be the only laptop in its class that still uses TN panel. And for a "best computer" it has a lauphably low resolution. Lack of 4G is annoying. Lack of touch screen option is inexcusable. In short, MBA is a solid mid-range laptop. More importantly OP made a very valid observation that lately AT stated giving Apple products way more credit than they deserve. Reply
  • vFunct - Sunday, July 07, 2013 - link

    No the MBA is perfect. Nobody wants a retina screen at that size, since the only people that use them are photographers and they have MBPros. No one wants 4g either since they tether anyways. And touch-screens are completely useless, so no one wants them either.

    Again, Apple makes the best laptops in the industry. They are perfect for their target audiences.
    Reply
  • lilo777 - Sunday, July 07, 2013 - link

    So the photographers want "retina" displays on the phones , iPads and MBPs but not MBAs. interesting. Also, what kind of photographers prefer TN panels to IPS panels? Reply
  • vFunct - Monday, July 08, 2013 - link

    Photographers use iPhones, iPads, and MacBook Pros. They DON'T use MacBook Airs.

    The people that buy MacBook Airs use them for email, office apps, and surfing the web. Those users have never wanted or cared about retina displays.

    So, this Retina display complaint is a non-complaint, since no one that would want a MacBook Air is going to complain about it.

    You guys need to learn the purpose of what you use a computer for.

    You don't buy a computer to own tech specs. You buy a computer as a tool to do what you want, and the people that want the MacBook Airs do not want a Retina display.
    Reply
  • icoltsfan94 - Tuesday, August 13, 2013 - link

    I disagree in the fact that MacBook Air potential buyers would not want a retina display. I personally have considered a MBA and one of the biggest turn-offs has been its 1366x768 display, even an upgrade to a 1920x1080 display would be an amazing upgrade, after all, the prevalence of HD content on the internet has significantly increased since the incarnation of the MBA, which has that same 1366x768 resolution at its release. Not to mention the ability to have multiple web pages open at the same time on one screen. Even then, if you have no desire for any of these items, having a higher resolution in the same screen size would allow for better rendered fonts and images in web pages even in just general web browsing. I would love to see an honest argument against having a higher resolution display in the MBA. Reply
  • bji - Sunday, July 07, 2013 - link

    Is "no touch screen option" actually a valid complaint about any laptop? Reply
  • gentux - Friday, July 26, 2013 - link

    Well the best display is useless if it has no juice left. Even Sony Vaio Pro has not that much battery power in it yet it's more expensive. Speaking of 4G you know how many different bands and providers there are in the world? And how that changes in the next 3 years a typical notebook is supposed to be used? It's better to keep that separate so you can use some tethering solutions abroad. Reply
  • GotThumbs - Monday, July 08, 2013 - link

    It's not hard when you (Apple) controls every aspect of its ecosystem. Software, OS, Hardware and marketplace are owned and controlled by Apple. You cannot load Apples OS onto any other hardware (Legally anyway), so they control/limit the hardware configuration and thus the number of drivers you need to have a stable system. Google Chrome Books actually are a similar option (IMO) and with more companies moving to cloud based software.....there is less need to actually install programs on your desktop/laptop.

    If MS decided to regulate Windows on systems of thier own design, you would have very stable systems from MS as well. Just simply think of the number of combinations of PC systems /components currently available. It's in the millions. How many models does Apple have? What are the differences between each one?

    Jobs was very smart, but I have as much respect for him as I do a sleazy car salesmen IMO. (Google: Steve Jobs, Wozniak, Breakout) . While I will never own an IProduct, I give the company credit for how much money they have raked in while offering very limited product lines and controlling the content market where the REAL money is to be made. Apple has made billions selling one phone with incremental improvements to its fan base. What other company wouldn't want to follow that kind of success? Thats why I believe MS has initiated mandatory accounts to load apps onto Win8. All businesses exist to make money for the investors/owners. Apple is NOT any different IMO.

    Best wishes,
    Reply
  • gentux - Friday, July 26, 2013 - link

    Actually Microsoft has a logo program that doesn't help make PCs any more stable. Just as PlaysForSure stood for something that's a joke since the failed Zune. Sorry but Microsoft wasn't good at anything. Nobody really cared about Windows until they forced you to buy it. Then everyone hated it until Apple had their systems and except for bigger companies and people who think they need to be other than everyone else are moving to OS X.

    If you ask people who used both they will stay with OS X that's the success Apple did.

    If that's not a big of a point why there's no one else?
    Reply
  • ESC2000 - Monday, August 12, 2013 - link

    If that was true - that people who have used both windows and OSX always stick with apple - apple's marketshare would be way higher. In the computer space its marketshare is puny even though it offers lower cost laptops than it used to. I count myself as one of the people who stuck with Windows. I had to use my sister's macbook pro for a semester in college after I spilled on my VAIO. That was a miserable semester for me computer-wise... couldn't wait to get back to windows. I am far from the only person who prefers windows. I see it when i look around the classroom and see way more windows computers (mostly high-end so people who could have bought the air at least) and I see it in every company/firm that I have ever worked for or even visited -literally none used OSX. So good try there.

    I get this shtick all the time on these tech sites: 'anybody who has ever used [insert iproduct here] will prefer it over other options and never go back to anything else.' We all know logically that absolutist statements like that cannot be true (saw another one a page back claiming that apple makes the best computers period). All one need do to disprove it is if course provide one example to the contrary.

    I know most of these statements are meant somewhat hyperbolically (although I also think people are apt to project their own experience onto every other person in the world). to the extent that they merely mean the trend is toward people abandoning windows for OSX, all I can say is it is not what I observe - whether computers, tablets (v. Android), or phones (again v. Android). But of course we see what we want to see and what we are looking for, so without hard numbers it is hard to know.
    Reply

Log in

Don't have an account? Sign up now