Battery Life

Testing battery life on a tablet is pretty grueling as these things are effectively smartphones with gigantic batteries. What would last for only a few hours on a smartphone can easily last over ten on a tablet. The iPad 2 is no exception.

As iFixit discovered, the iPad 2 features a nearly identical battery to the original iPad (25Wh vs. 24.8Wh). We already established that display brightness hasn't gone up so the only real impact on battery life will be because of the A5 SoC.


The iPad 2 WiFi's battery, courtesy iFixit

The ARM Cortex A9 tends to be more power efficient than its predecessor, the A8. With a shallower pipeline and the ability to execute instructions out of program order you get better performance per watt in most cases. As a result the A5 should complete bursts of instructions quicker than the A4 and get back to sleep sooner.

To put this to the test we put together a battery life test that combined our non-Flash smartphone web browsing test, checking for email every 15 minutes (via a Gmail account receiving ~100 emails per day) and constant local music playback while all of this is going on. The results are pretty much as expected:

General Usage - Web Browsing, Email & Music Playback

Over WiFi the Motorola Xoom and iPad 1 deliver very similar results. The iPad 2 pulls ahead by around 8%, it's not a huge advantage but it's there. Over 3G there's a noticeable drop in battery life, putting both of the iPad 2s below 10 hours and kicking the Xoom down to under 9 hours. All of the numbers on this chart are respectable however and you can expect a good day's worth of use out of any of these tablets.

Note that while the iPad 2 did better than its predecessor if you were to run an app that pegged both CPU cores at 100% you'd see reduced battery life on the iPad 2 vs. the iPad 1. Granted you'd also see better performance on the iPad 2.

Video playback is obviously an important function of these new tablets so we put together a H.264 decode playback test as well. For this test we transcoded a copy of Quantum of Solace from a 1080p BD source down to a 720p H.264 using Handbrake's Normal encode profile with one modification. In order to enable smooth playback on the Motorola Xoom we had to disable b-frames in the encode. The results are below:

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

The iPad 2 consistently lasted longer than the original iPad in our video playback test. The Xoom however did noticeably worse. Unfortunately only a portion of the H.264 decode pipeline is accelerated by NVIDIA's Tegra 2 in this test. When playing back anything more strenuous, portions of the pipeline are handled by the CPU cores in software. If you were to enable b-frames the Xoom would not only stutter but its battery life would drop to around 6 hours.

On the iPad 2 its Cortex A9s are mostly powered down during this test, on the Xoom the A9s are helping with the heavy lifting for video decode and as a result we see lower battery life. Kal-El is expected to address this issue head on.

The GPU: Apple's Gift to Game Developers HDMI Mirroring & Charging
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  • podperson - Monday, March 21, 2011 - link

    Just admit that most PCs are used as toys. Heck, the whole reason the personal computer took off (in homes) was as a games platform.

    Most of the people I see with PCs are using them to surf the web, watch youtube, update facebook, or mess around with digital media. Where I work there are Macs and PCs available to the public with 27" monitors all open to Facebook (hint, it's a university). Exactly what is this "work" you need to do on PCs? For most people it's a little bit of text editing now.

    For some kinds of things the iPad is markedly superior ergonomically to a PC (or even a tablet computer or WACOM tablet display) — e.g. sketching or various musical apps. For others a PC is markedly superior. For still others one or the other is completely useless.
    Reply
  • michael2k - Monday, March 21, 2011 - link

    Except it isn't bulky nor underpowered for many things.

    I have a 2006 G4 iBook that is lower performance than a 2010 iPad 2. If the iPad 2 is a toy, then so is just about any early 2006 computer, including older Pentium M based laptops.

    It is also far less bulky than self same 4 year old computers, with trivially 2 to 3 times the battery life.

    I paid $500 so that my wife can follow my kids around, but still have a computer she can put in her purse. Without the iPad, she would have indeed settled for an iPod touch, but a netbook with a hinge? Too short a battery life and too hard to manage (Windows XP, Windows Update, AV, etc) for the harried housewife/homemaker
    Reply
  • bigboxes - Monday, March 21, 2011 - link

    Just how big is her purse? As for battery life I think you are looking through rose colored glasses in emphasizing the positive qualities that your device holds. As long as the device lasts until you get home to plug it in (maybe even your vehicle) it will suffice. The iPad is too bulky and not functional enough too do day to day tasks. As I said earlier, the authors point this out.

    As much as we want these cute devices to succeed we find ourselves using other devices that are far more practical. I've made the same mistake myself in the past. Anyone remember the Sony Clie? Another proprietary underpowered overpriced device. I believe I paid $500 for it. It gathered dust for years until I finally put it in a box. There's the cool factor and then there's reality. Do you set it out for your friends' visits or do you actually get x value out of it?

    Also, you are going to be carrying your phone with you already. Why carry both devices with you when one doesn't have more functionality over the other? I would think that the balance for function belongs to the smartphone (phone service is more valuable than screen size).
    Reply
  • michael2k - Monday, March 21, 2011 - link

    Her purse is big enough to hold an iPad, a wallet, another smaller purse, a phone, keys, two Capri Suns, two candy bars, a small bag of chips, and a couple of diapers.

    As for battery life, that's exactly what the iPad is; it lasts as long as it needs to until it gets home to be plugged in. I cannot find a laptop under 2 pounds with similar battery life. The minimum requirement is 6 hours.

    I carry my phone because I am more like Anand than not. She carries the iPad because she isn't like Anand, at all. It would be the equivalent of me driving a Civic and her driving a minivan; surely the very concept of a soccer mom and her requirements being different than a 9-5 commuter isn't lost on you?
    Reply
  • bigboxes - Monday, March 21, 2011 - link

    So, we can officially say this is the official tablet of soccer moms everywhere. Yay.

    She carries it around not because she is unlike Anand. She carries it around because she has a strong back!
    Reply
  • vol7ron - Sunday, March 20, 2011 - link

    A lot of the "sales" are from the retail outlets and not-necessarily the end-user consumer. There's people that buy it to sell to China or other Asian countries that buy it for double it's price; there are a plethora of reviewers these days; there are the people with mass amount of wealth that buy up anything just because they can; and then the hipsters that want to be cool and fit in. It reminds me of the episode of South Park with the smug Prius drivers.

    I'm not saying this isn't a bad device and it's mobility makes it beneficial in many regards. But the price of its mobility does not make it as attractive as it would be at the lower price (~$250). I'm not saying it should go for $100, but you're nearing the $1000 end of the spectrum for these devices and way over that for the necessary apps and accessories.
    Reply
  • crunc - Monday, March 21, 2011 - link

    I don't know why I'm getting into this argument, but all the iPads, including iPad 2's, that I'm seeing out in the world would seem to dispell your notion that no one is actually buying them for their own use. I saw 3 of them within 5 feet of me on the train this morning, for example. In 3 weeks time or so I'll be another one on the train with one, and also using it at home. I don't own a laptop. I wouldn't mind a laptop, but I'd rather have an iPad. It is, for me, far more comfortable to use then a laptop. Even the excellent trackpads on MacBooks don't compare to the entirely touch-based interface of the iPad. Obviously they aren't for everyone, but for some these are a great choice. I don't expect to write a book on it, but I then don't write books. If I ever decide to write a book, maybe I'll get a laptop. Reply
  • Ushio01 - Sunday, March 20, 2011 - link

    It's a fasion accessory just like the iphone, to be with the "in crowd" you have to have apple products that's all there is to it. Everyone on here must know at least someone who bought an iphone and then use it only for calls and texts, I know dozens of people who have done this. Reply
  • crunc - Monday, March 21, 2011 - link

    Actually, no, I don't know anyone who has an iPhone that only uses it for texts and phone calls. Everybody I know who has one uses it for virtually everything, myself included. In fact, I rarely text and only occasionally make phone calls (mostly of the, "should I pick up a pizza?" variety). You go on living in your little dream world, though. I won't stop you. I have an order in for an iPad 2 and I'm really looking forward to it. I love my iPhone and I want something akin to a laptop, but that isn't that, because the iOS interface is fantastic and the devices are more comfortable for me to use. Sure, there's some shortcomings to the platform, but they are overwhelmed by the multitude of positives. Reply
  • sarahtim - Sunday, March 20, 2011 - link

    I think this sort of comment represents a failure of imagination. As iPads sell million after million you have to adjust your idea of how many hipsters there are...
    Other people are different from you.
    Speaking for myself; I find my iPad extremely useful. I use it for a number of hours each day. I don't find it clunky. To me, and this is a very personal thing, the cost was of little consequence. While it is poor taste to blurt out your relative wealth when many folks are having a rough time of it, it is the only way to answer your comment. Further, I consider iPads to be very good value. I bought the bottom of the line iPad 1. It does everything I want. The bulk of its time is spent streaming video via the Air Video app.
    I represent a single data point - as do you. I fully appreciate that an iPad is a useless paperweight to you. No problem. When I use my iPad I do it in private. I don't discuss my ownership with others. I don't think I'm clever or a better person because I have one.
    You would have to look at me for a very long time before you thought of a hipster. Trust me on this. :-)
    Reply

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