Battery Life Explored

Last week I did a quick preview article showing some initial battery life results for Windows 8 Consumer Preview. What started as just one set of results from one battery life test quickly ballooned into more in-depth testing, as the first results were rather shocking. Eventually, I added a second laptop to the list and started running additional tests on both laptops. Below you can see the full set of results, but let me preface the charts with some additional information that may help to explain any discrepancies between our results and those you might find elsewhere.

My initial test was done after performing an in-place upgrade to Windows 8 CP on a laptop that had been used on and off for the past year. The laptop was the original quad-core Sandy Bridge sample that Intel shipped out to various sites last year; to the best of my knowledge, the laptop was never actually sold at retail, though it’s similar to older Gateway NV7x models and sports a “Packard Bell” logo on the touchpad buttons. Quite a few games and applications had been installed (and uninstalled) during previous benchmarking, but I figured an in-place upgrade would be representative of what many will do. I had hoped to return and do a completely clean install as well, but that eventually proved unnecessary (and I didn’t have enough time). What I do know is that I ran the Internet Explorer 10 CP test three times on that initial upgrade, and outside of the first run (240 minutes), the other two results were virtually identical (262 and 263 minutes).

For some reason, doing an upgrade to Win8CP with a “well worn” installation of Windows 7 appears to have the potential to seriously impact battery life. After doing a clean install of Windows 7 and re-testing all battery life results (to ensure battery degradation wasn’t penalizing the Win8 scores relative to our original Win7 results), I then performed a second upgrade to Win8CP. This time, the results were far better on the IE10CP test, but other than installing all the drivers and Windows Updates, the only applications on the laptop outside of the standard Windows install are Chrome 17, 7-Zip, and a few other small apps like MPC-HC and VLC. So basically, the second Win8CP upgrade appears to be analogous to a clean install of Windows 8.

In order to have a second set of data, I did perform a completely clean install of Windows 8 CP on a second laptop, the ASUS K53E (which also came to us via Intel last year). I did a clean Windows 7 install on a 64GB Kingston V100 SSDNow, ran all our tests (again to verify that battery degradation isn’t playing a role), switched to a second V100 SSD and did a clean install of Windows 8 CP, and then ran all the tests again. Given the time constraints, I was not able to run all of the tests multiple times, so the margin of error is perhaps as much as 5%, but I did run several of the tests more than once and variation between runs was typically less than 1%. Note that the hardware used for the battery life testing is completely separate from all the other tests; below are the brief specs tables for the two test laptops:

ASUS K53E Specifications
Processor Intel Core i5-2520M
(2x2.50GHz + HTT, 3.2GHz Turbo, 32nm, 3MB L3, 35W)
Chipset Intel HM65
Memory 1x4GB + 1x2GB DDR3-1333 CL9 (Max 8GB)
Graphics Intel HD 3000 Graphics (Sandy Bridge)
12 EUs, 650-1300MHz Core
Display 15.6" WLED Glossy 16:9 768p (1366x768)
(AU Optronics B156XW02 v6)
Hard Drive(s) 64GB SSD
(Kingston SSDNow V100)
Optical Drive DVDRW (Matshita UJ8A0ASW)
Networking Gigabit Ethernet (Atheros AR8151)
802.11bgn (Intel Advanced-N 6230, 300Mbps capable)
Bluetooth 2.1+EDR (Intel 6230)
Battery 6-Cell, 10.8V, 5.2Ah, 56Wh

 

Compal Sandy Bridge Notebook Specifications
Processor Intel Core i7-2820QM
(4x2.30GHz, 32nm, 8MB L3, Turbo to 3.40GHz, 45W)
Chipset Intel HM65
Memory 2x2GB DDR3-1600 (Max 8GB)
Graphics Intel HD Graphics 3000
12 EUs, 650-1300MHz Core/Shader clocks
Display 17.3" LED Glossy 16:9 HD+ (1600x900)
(Seiko Epson 173KT)
Hard Drive(s) 160GB SSD (Intel X25-M G2 SA2M160G2GC)
Optical Drive BD-ROM/DVDRW Combo (HL-DT-ST CT21N)
Networking Gigabit Ethernet (Atheros AR8151 PCIe)
802.11n (Centrino Wireless-N 1030)
Bluetooth 2.1+EDR
Battery 8-Cell, 14.8V, 4.8Ah, 71Wh

With two laptops running clean installs of Windows 7 and Windows 8 Consumer Preview, I think it’s safe to say that our tests are representative of what you can expect from the current release. However, that doesn’t mean the results are what we can expect when Windows 8 finally ships. Drivers and optimizations from laptop manufacturers can certainly improve the results. Beyond the clean installs, to make sure that we’re doing an apples to apples comparison, I configured all of the power settings identically between the two OSes. We’re using the Power Saver profile, with the following settings (the one difference being the display brightness, which was calibrated to 100nits on both laptops—50% brightness on the K53E and 40% on the Compal):

The laptops being tested have been running battery life tests (or recharging) pretty much constantly for the past week, and I’ve only just completed the results for both OSes using one set of power settings. There are low-level differences between the Power Saver and Balanced profiles that can and will impact both performance and battery life. Previous testing has shown that Power Saver typically improves battery life by a few percent, even with all other settings identical, and the CPU performance appears to vary quite a bit depending on the workload. I also disabled Intel’s Display Power Saving Technology for both laptops in Windows 7 (I can’t seem to find a way to check this in Windows 8 right now); when enabled, DPST will adjust contrast and brightness to try and improve battery life, but there is a loss in image quality and it has the potential to introduce more variation between runs.

So with that out of the way, we now have a full suite of battery life results from Windows 7 and Windows 8 Consumer Preview. Again, the early nature of the OS and drivers mean that these results can and very likely will change by the time Windows 8 ships later this year. We could also look at using the Metro version of IE10CP on Windows 8, but that would entail tweaking our tests to get it to work so we’ll save that for another day. Here are the full details of our test settings/scripts:

Idle Battery Life: We start a timer that outputs the current time to a text file every minute, then unplug the laptop. WiFi is disabled and audio is muted for this test.

Heavy Web Browsing: We start a script that outputs the current time to a text file each minute, and it also launches the web browser, kills it after 55 seconds, and relaunches it 5 seconds later. We load up four web pages with Flash content (mostly advertisements) in the test browser—IE9, IE10CP, and Chrome 17 for this article. WiFi is enabled and audio is muted for this test.

H.264 Video: We use the same timer script as the idle test, but this time we launch a video player with an H.264 encoded HD video right after unplugging the laptop. We tested with Media Player Classic Home Cinema x64 (version 1.6.0.4014) and VLC (version 2.0.0). The video used for these tests is a 720p High profile 5.1 encode with a 5.56 Kbps video stream and 6-channel DTS 1.5 Kbps audio bitstream. We set the video player to loop, disable WiFi, unmute audio, plug in a set of headphones, and set the volume to 40%.

Battery Life—Idle

Battery Life—Heavy Web Browsing

Battery Life—Heavy Web Browsing

Battery Life—H.264 Video

Battery Life—H.264 Video

The overall results with our current test laptops have Windows 7 delivering better battery life in most instances. On the ASUS K53E, the advantage ranges from 4% in VLC to as much as 15% in Internet Explorer, but the comparison between IE9 and IE10CP could skew that result more than in other tests. Chrome 17 gives Win7 a 10% advantage, idle battery life is 10.5% better, and MPC-HC battery life is 8% better.

Switch to the Compal notebook and we actually get one discipline where Windows 8 CP comes out ahead: video playback. It’s not exactly clear why the quad-core laptop does better under Win8 in this area, but both VLC and MPC-HC last longer than on Win7—3% longer with VLC and 6% longer with MPC-HC. Elsewhere, however, the lead for Win7 over Win8CP continues. Idle battery life is 6% better, Chrome 17 is 4% better, and in IE9 vs. IE10CP Win7 leads by 14%.

Given that there’s always slight variation between battery life runs, anything less than 3% is probably nothing to worry about, especially considering the early nature of the Win8CP release. Microsoft could easily close the gap by the time the OS ships, and with additional optimizations Windows 8 could even take the lead in most of our benchmarks. Even a 15-20% deficit with IE10CP could disappear by the time the application and OS are fully optimized, and hopefully our earlier experience where Internet battery life for a "well used" Win7 to Win8 upgrades dropped an additional 25% will get worked out.

I should also point out that the use of Flash in the browser battery life tests could be having a very significant impact on IE10CP. I noticed during the tests that the browser loads the pages much more slowly than in IE9 at times—e.g. sometimes it will take upwards of 20 seconds for the main page (a cached version of AnandTech.com) to load, where most other times the page will load in less than five seconds.

Relative Battery Life—Idle

Relative Battery Life—Heavy Web Browsing

Relative Battery Life—Heavy Web Browsing

Relative Battery Life—H.264 Video

Relative Battery Life—H.264 Video

Along with our pure battery life results, we also calculated normalized battery life for the same tests. The ASUS K53E has a 56Wh battery and the Compal notebook has a 71Wh battery, so we simply divide the number of minutes by battery capacity. As expected, the K53E takes the lead over the Compal in all of the normalized battery life results. It has a smaller LCD (and a lower resolution), giving it a particularly large advantage in things like full screen video.

Obviously, we’re still only looking at two laptops, and there are many types of laptop that we haven’t been able to test with Windows 8 CP. Just to list a few items that we can’t comment on right now, we didn’t look at battery life with discrete GPUs from AMD or NVIDIA. Drivers and WDDM1.2 have the potential to change things even more for such laptops. Likewise, we didn’t look at any switchable graphics laptops (NVIDIA Optimus or AMD Dynamic/Manual Switchable). I don't have any AMD-based laptops right now that I can test Win8 on, so the two laptops are relatively recent Sandy Bridge models. All of our current test results also come from laptops with SSDs; my experience in the past two years is that SSD vs. HDD doesn’t make much of a difference for battery life unless you’re specifically placing a moderate to large load on the storage subsystem, but there’s still a chance for something to change.

Long story short [Ed: Too late!], Windows 8 Consumer Preview currently shows slightly lower battery life in most of our tests compared to Windows 7, and Internet Explorer 10 CP shows quite a bit worse battery life than IE9. We wouldn’t worry too much about the drop at this point, though again it’s worth noting that certain combinations of hardware and software could show a larger change than what we experienced—for better or for worse. If you need every last bit of battery life, we’d recommend keeping a backup of your Windows 7 installation handy in case things go wrong with Windows 8 CP, but for typical users and those interested in checking out how Windows 8 is shaping up, factors other than battery life are likely going to be more important to your overall experience.

If there’s any specific type of laptop you’d still like to see us test with Win8CP that we haven’t covered with these two laptops, let us know and we’ll see what we can do, but no promises—we’ve probably already gone overboard with battery life testing on a beta OS! Likewise, if there are other battery life tests you’d like us to run on these two laptops, we can look at that as well. Just let us know what you’d like to see and we’ll try to make it happen.

Boot Time and Memory Usage System Requirements and Recommendations
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  • yannigr - Friday, March 9, 2012 - link

    This is more of a funny post but.... do you hate AMD systems? Are AMD processors extinct? I mean 8 systems ALL with Intel cpus? Come on. Test an AMD system JUST FOR FUN..... We will not tell Intel. It will be a secret. :p Reply
  • Gothmoth - Friday, March 9, 2012 - link

    AMD?

    who is still using AMD?
    except some poor in third world countrys?

    no.. im just joking... AMD is great and makes intel cheaper.. if only they would be a real competition.

    but what about ARM?
    that would be more interesting.. but i guess we have to wait for that.
    Reply
  • JarredWalton - Friday, March 9, 2012 - link

    In defense of Andrew's choice of CPU, you'll note that there's only one desktop system and the rest are laptops. Sorry to break it to you, but Intel has been the superior laptop choice ever since Pentium M came to market. Llano and Brazos are the first really viable AMD-based laptops, and both of those are less than a year old. AFAIK, Andrew actually purchased (or received from some other job) the laptops he used for testing, and they're all at least a year old. Obviously, the MacBook stuff doesn't use AMD CPUs, so that's three of the systems.

    As for the two laptops I tested, they're also Intel-based, but I only have one laptop with an AMD processor right now, and it's a bit of a weirdo (it's the Llano sample I received from AMD). I wouldn't want to test that with a beta OS, simply because it's likely to have driver issues and potentially other wonkiness. Rest assured we'll be looking at AMD systems and laptops when Win8 is final, but in the meantime the only thing likely to be different is performance, and that's a well-trod path.
    Reply
  • DiscoWade - Friday, March 9, 2012 - link

    Last year, I needed to buy a new laptop. I wanted a Blu-Ray drive and a video card. I thought I would have to settle for a $1000 computer with an Intel processor. I had narrowed my choices down to a few all with the Intel i-series CPU. When I went to test some out at Best Buy, because I wanted to play with the computer to see if I liked it, I saw a discontinued HP laptop on sale for $550. It was marked down from $700. It had the AMD A8 Fusion CPU and a video card and a Blu-Ray drive. So I got a quad-core CPU with 4 hour actual battery life that runs like a dream very cheap. I was a little apprehensive at first with buying the AMD CPU, but a few days of use allayed my fears.

    If you say Intel makes better laptop CPU's, you haven't used the AMD A series CPU. It has great battery life and it runs great. How often will I use my laptop for encoding video and music? The dual-AMD graphics is really nice. Whenever I run a new program, it prompts which graphic card to use, the discrete for power savings or the video card for maximum performance. I like that.

    Yes if I wanted more power, the Intel is the way to go. But my laptop isn't meant for that. And most people don't need the extra performance from an Intel CPU. Every AMD A8 and A6 I've used runs just as good for my customers and friends who don't need the extra performance of an Intel.

    However, I haven't yet been successful installing my TechNet copy of W8CP on this laptop. I'm going to try again this weekend while watching lots of college basketball. (I love March Madness!) If anybody can help, I would appreciate if you let me know at this link:
    http://answers.microsoft.com/en-us/windows/forum/w...
    Reply
  • MrSpadge - Friday, March 9, 2012 - link

    You do realize that Jared explicitely excluded Llano and Brazos from his comment? A8, A6, A4 - they're all Llano. Reply
  • Samus - Monday, March 12, 2012 - link

    I'm actually shocked he didn't use an AMD E-series laptop (HP DM1z, Lenovo x120/x130, etc) as they have sold hundreds of thousands in the last 12 months. I see a DM1z every time I'm in an airport, and x120's are very commonplace in education.

    Remembering the Sandybridge chipset recall last year, this really gave AMD a head start selling low power, long battery life laptops, and they have sold very well, and belong in this review when you consider the only laptops you can buy new for <$400 are AMD laptops, and that is a huge market.
    Reply
  • silverblue - Monday, March 12, 2012 - link

    This isn't a review. Also, he didn't have one.

    Quite open to somebody benching a DM1z on W8CP, though. ;)
    Reply
  • phoenix_rizzen - Friday, March 9, 2012 - link

    While Intel may have the better performance CPU in laptops, they have the *worst* (integrated) graphics possible in laptops, and have 0 presence in the sub-$500 CDN market.

    You'd be surprised how many people actually use AMD-based laptops, especially up here in Canada, mainly for three reasons:
    - CPU is "good enough"
    - good quality graphics are more important than uber-fast CPU
    - you can't beat the price (17" and 19" laptops with HD4000+ graphics for under $500 CDN, when the least expensive Intel-based laptop has crap graphics and starts at over $700 CDN)
    Reply
  • frozentundra123456 - Friday, March 9, 2012 - link

    A bit confused by your post. What is HD 4000 graphics? Granted Llano is superior to SB, but Llano is 66xx series isnt it? I though AMD 4000 series was a motherboard integrated graphics solution that is very weak. Intel SB graphics will be far superior to any integrated solution except Llano.

    I agree for my use, I would buy Llano in a laptop ( and only in a laptop) because I want to do some light gaming, but I dont understand your post. I would also not really call SB graphics "crap" unless you want to play games.
    Reply
  • inighthawki - Friday, March 9, 2012 - link

    HD 4000 is referring to the intel integrated graphics on the new ivy bridge chips - nothing to do with AMD chips Reply

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