The Final Word on Battery Life

In our iPhone 4S review I mentioned that our web browsing battery life tests were in dire need of an update. The move to iOS 5 increased the aggressiveness of browser side caching, which impacted our old tests significantly. We still have plans for a much more significant departure from our existing battery life testing methodology, however as an interim solution I developed a modified version of our traditional smartphone battery life test.

The old web browsing test lacked any significant cache busting features and the HTML workload itself was more representative of mobile sites than a full desktop experience. The modified test does a much better job of not allowing its components to be cached by the browser, and includes both lighter and full desktop websites. Since the workload has changed, these numbers are no longer comparable to those running the older version of our test. The new web browsing test is also stressful enough to span both smartphones and tablets, whereas before we had a separate version just for tablets.

Finally, I must mention that we ensure all tablets tested here are normalized to the same display brightness setting of 200 nits for a true apples to apples comparison. As always we rely on the stock web browser that ships with the platform and manually quit all background tasks before running our tests. In the case of the Transformer Prime, I was able to run our new battery life test using all three power profiles to get a better idea of the range of battery life. As a recap, here are the details on the power profiles.

ASUS and NVIDIA have defined three power profiles on the Prime: Normal, Balanced, and Power Saving. Normal allows the CPU to run at up to 1.4GHz with only a single core active, and 1.3GHz otherwise. Balanced is the default setting and it drops maximum CPU clock to 1.2GHz and favors lower clock/voltage targets on the curve compared to Normal mode. Power Saving caps CPU frequency at 1GHz with 1—2 cores active, 760MHz with 3 cores active and 620MHz with 4 cores active. It's unclear what the impact is on GPU clocks/performance. I've also noticed that the Power Saving profile also enables a dynamic contrast control that you can't override.

Web Browsing Battery Life

The shipping Prime does much better than the original tablet I reviewed a couple of weeks ago. It's clear that whatever was impacting WiFi performance also took its toll on battery life. What I suspected might be the case ended up being true: the implementation of Tegra 3 in the Transformer Prime delivers better battery life than Tegra 2 in the original Eee Pad Transformer. There are too many variables here for me to attribute the gains to NVIDIA's SoC alone, but seeing as how battery capacity hasn't changed it's likely that we do have Tegra 3 to thank for better battery life in the TF Prime.

Note that even running in Normal mode and allowing all four cores to run at up to 1.3GHz, Tegra 3 is able to post better battery life than Tegra 2. I suspect this is because NVIDIA is able to parallelize some of the web page loading process across all four cores, delivering similar performance to the original Transformer but at lower frequency/voltage settings across all of the cores. Additional performance gained by supporting NEON likely helps improve efficiency, not to mention higher single-threaded performance thanks to Tegra 3's higher clocks. Combine all of this with a more mature 40nm process and a more mature Cortex A9 implementation on that process, and the power improvements make sense.

The Transformer Prime is still unable to dethrone the iPad 2 here, which just goes to show you how efficient Apple's platform was to begin with. That being said, the Prime is within striking distance of Apple's tablet. The race is now close enough where you won't notice too much of a difference between the two.

There's also not a huge difference in battery life between the various power profiles. I do applaud ASUS and NVIDIA for giving us control over the CPU governor, but unless you're trying to make the tablet last over a very long flight you're probably fine just leaving it in Normal mode and enjoying the extra performance.

I included results from the Prime running with its dock attached. The additional 22Wh battery improved battery life by 51%. The scaling isn't linear because the dock itself draws power. Once the dock's battery is depleted, the tablet needs to power both itself and the dock. The improvement is tangible though, if you need to do a lot of writing on a flight around the world the dock will help you get there.

Video playback battery life is much better than the original Eee Pad Transformer. Tegra 2 was clearly broken when it came to its video decode abilities and as a result we saw significant limitations on both what video you could play and how long you could play them. Tegra 3 fixes all of that, and the result is battery life that's getting closer to the iPad 2:

Video Playback—H.264 720p Base Profile (No B-Frames)

Getting 11 hours of continuous video playback battery life is something to be proud of. Being able to watch 4-6 full length movies on a plane without worrying about your battery is a pretty nice feature. Unlike the active use case, video playback seems to see a bigger benefit from switching away from the Normal power profile.

 

Super IPS+ & Color Gamut Changes to the Browser & Performance Analysis
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  • Alienate - Friday, December 16, 2011 - link

    So, if I buy one of these now, will I be able to upgrade to Icecream ?

    If so, how?
    Reply
  • niteflyguy - Friday, December 16, 2011 - link

    My one concern is the single speaker. How doesit sound? Reply
  • stelek - Saturday, December 24, 2011 - link

    Hi Anand,
    Have you tested the GPS performance? Does it work? What's the accuracy?

    The first users report some serious problems and for me this is definitely a deal breaker. Could you please verify that? Please see here:
    http://forum.xda-developers.com/showthread.php?t=1...

    I'm supposed to pick up my pre-order in a few days. But I'm not gonna do that unless I know that GPS is not broken in Prime.
    Reply
  • Krewe - Monday, January 02, 2012 - link

    A brain injury rewired my hearing so that fan noise from computers/TVs/etc can literally cause me to leave the room.

    To Anand or anyone who is absolutely sure on this issue, are there fan(s) in the original Transformer or Prime or their Docks?

    Many thanks in advance.

    Krewe
    Reply
  • Krewe - Saturday, January 07, 2012 - link

    Anand,

    Thank you for the Transformer Prime teardown. Your attention to the Prime's fanless heat dissipation was not lost on me.

    Krewe
    Reply
  • shopscounty - Monday, January 09, 2012 - link

    Surely you will find on ShopsCounty. You can buy a <a href="http://www.shopscounty.com">ASUS Transformer</a> at ShopsCounty. Reply
  • kulpret - Saturday, March 03, 2012 - link

    Anand,

    Would love to see an update to your review now that ICS has been on this tablet for awhile. I personally haven't touched my iPad2 since I received my TP. I use it in place of my laptop and netbook as well. I rarely have to pick up anything else. I am a road warrior with a Verizon MiFi and Sprint Hotspot on my phone and always have internet connectivity and this thing is always with me.

    Games:

    Between onlive, emulators and all the gaming options from Android (including the great Tegrazone games) this makes the case for a mobile gaming platform with console quality graphics but also the dead simple casual gaming making this a great fit for both types of gamers. Onlive is excellent on this platform btw.

    Productivity/Web:

    I just recently added Onlive Desktop to my subscription and I have full blown Office at my finger tips along with Internet Explorer. It is limited to the MS stack on the desktop, but I find that good enough. Native to the tablet I use Polaris Office, Adobe, Firefox, Chrome, Android Browser and Dolphin. I literally have not found office content that I can't access. The same is true for web content including Flash support.

    Media:

    All the usual app suspects are here. Netflix, Pandora, Hulu + (installs but doesn't officially support the device takes a little bit of know-how to get it working. ie developer mode and config files.) One must have app for Android here MX Video Player It plays all my years of movie collecting, works as good as VLC on Windows/Linux.

    I also have this working with my ActiveSync Mail server for my corporation and actively use this device for presentations and note taking in customer meetings.

    I only hope they continue to develop and support the Transformer platform and I only see a bright future for this tablet.

    -Jon
    Reply
  • gmulak - Saturday, March 31, 2012 - link

    What a great review. Very detailed and complete. I do agree a signoff would be nice. I have had a little trouble finding out about battery "memory", I didn't catch that in the review, which would have been nice. Finally found what I think is correct on Asus web site. It is best to let the tablet discharge completely and then recharge it. I will definitely follow you. Great job. Reply

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