Battery Life

For a company that has been so laser focused on reducing weight and device thickness, the new iPad actually growing in both of these dimensions was unexpected. From a technical standpoint, the tradeoff makes sense. The new Retina Display consumes significantly more power than its predecessor, as do the A5X and MDM9600 baseband. Both of those ASICs are still built on a 4x-nm LP process and will surely increase power consumption over the iPad 2.

With more transistors switching on the same process node and a display (and backlight) driving more pixels at the same brightness, the battery either had to be larger or battery life would suffer. Apple understandably chose the former and the new iPad ships with a 42.5Wh battery—the largest we've ever seen used in an ARM tablet. The new iPad's battery is so large it's even bigger than what Apple uses in the 11-inch MacBook Air, and it's within striking distance of the 50Wh unit you'll find in the 13-inch model. I do believe this move says a lot about how Apple sees the iPad moving up in the world, but I'll get to a discussion about that later.

With a 70% larger battery than the iPad 2 but with more power hungry components inside, how does the new iPad fare in real world usage? Subjectively: it doesn't last as long as its predecessor. Objectively, our numbers seem to agree.

Our web browsing battery life test browses through dozens of web pages, pausing on each to simulate reading time, until the battery is depleted. All of our tests are run at the same brightness settings (200 nits) to ensure we are comparing apples to apples.

Web Browsing Battery Life

On WiFi we measured an 8% decrease in battery life compared to the iPad 2—nothing huge but not insignificant either. Fall off of WiFi and depend on LTE and you'll see around a 9% decrease in battery life, again—noticeable but not unusable.

I also threw in numbers from the Motorola Xyboard 10.1, an LTE enabled Android tablet running 3.2. Equipped with a much smaller battery (~26Wh), the Xyboard 10.1 delivered 7.31 hours in our LTE web browsing test. The new iPad managed to last 16% longer on a single charge—a smaller advantage than you'd expect given the 70% increase in battery capacity, showing just how much power the new Retina Display and its backlight consume.

The iPad is more than usable on long flights or throughout the day without being tethered to a wall outlet, but in practice you can expect a decrease in battery life compared to last year's model.

Keep in mind that these values are all at 200 nits (roughly 70% brightness on the iPad). If you use the iPad at max brightness (~400 nits) you'll see considerably lower numbers:

Web Browsing Battery Life

In our web browsing test, at max brightness, we saw 5 hours and 34 minutes of continuous use before the battery died. The iPad 2 incurs a similar penalty, lasting under 7 hours in the same test. Do keep this in mind if you need to get a lot of untethered use out of the new iPad. In order to come close to Apple's battery life estimates you'll have to be below 70% brightness.

Charging

Despite the significant increase in battery capacity, Apple continues to ship the new iPad with the same 10W USB power adapter as the previous two models. You can charge the iPad via a Mac/PC USB port that implements the USB charging spec, however doing so will take a minor eternity to fully charge the tablet. Just as before, the new iPad will not charge off of a USB port if the tablet is awake; it will only charge when locked/asleep. The convenience of having a USB based charger is evident, but you'll want to stick with the 10W adapter to actually charge the iPad.

Charging the larger battery does take longer. If we measure from a completely dead state to when the iPad indicates that it's fully charged the increase in time is approximately 50%, from 4 hours with the iPad 2 to 6 hours with the new iPad. ASUS' Transformer Prime, by comparison, requires only 2.5 hours as it ships with an 18W charger. And no, you can't use ASUS' charger to speed up charge times on the new iPad—when connected, the TF Prime charger will only supply 9W to the iPad.

Charge Time

The story doesn't end there however. While the iPad 2 will draw 0W after its 4 hour charge cycle is complete, the new iPad will continue to draw around 3W after it claims to be fully charged. This will continue for roughly another hour at which point the power adapter will draw anywhere from 0.1—0.6W.

Note that when running at full brightness and with a heavy GPU load (e.g. Infinity Blade 2), the power adapter can't supply enough to keep the iPad charged and drive the display/internal components. 

There's no good solution here other than for Apple to start shipping the iPad with a higher wattage power adapter. I do believe faster charge times are going to be necessary if Apple is keen on sticking with this larger battery, not to mention the usage issues of not being able to maintain charge equilibrium under load.

Thermals

The increase in power consumption of the new iPad also manifests in the form of increased heat production. A 163mm^2 SoC built on a 45nm LP process is a serious chip. Although it doesn't run hot enough to require active cooling, the SoC alone is responsible for a couple of watts of the iPad's TDP under heavy load. Combine that with a 45nm LTE modem and the heat put off by the more powerful backlight and you've got a recipe for a noticeably warmer device.

Does the new iPad get warmer than the previous one? Absolutely. I would even go as far as to say that it can get uncomfortably warm, but it never gets too hot to hold. If you've used any of the modern Mac notebooks, I don't believe it's anywhere near as bad.

When holding the new iPad in portrait mode, with the home button at the bottom, the lower left corner of the device ends up being the warmest. Along the left edge of the iPad is where the logic board resides, and the lower half is home to the A5X SoC. Under load, particularly a heavy GPU load (e.g. playing a 3D game), this area is going to heat up quickly.

I took several measurements using a contactless IR thermometer in the same ambient conditions on a new iPad vs. the iPad 2. The results are below:

Thermal Comparison (Max Temperature)
  iPad 2 iPad (3rd generation)
Web Browsing (2 hours) 32.7˚C 37.6˚C
Infinity Blade 2 (1 hour) 34.2˚C 41.9˚C

Again, I don't believe this is a deal breaker but it's the obvious result of remaining on Samsung's 45nm LP process combined with a more power hungry display/backlight. I suspect there will be improvements in efficiency on the display side over time, but I can't see the Retina Display being any lower power than the iPad 2's 1024 x 768 screen. The real avenue for improvement will be when Apple shifts to 28/32nm silicon for the SoC and LTE modem. If you want a cooler running iPad, you'll have to wait until next year for that.

Handheld Image Editing: iPhoto for iOS The A5X SoC
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  • antef - Wednesday, March 28, 2012 - link

    Yes it's nice, no one will argue that. But I don't see it as the huge advancement the authors indicate. Using it in the store it seemed fine, but honestly just walking right up to it, I wasn't even sure if I was using the new or old iPad. I had to go over to the iPad 2 to recognize the difference. And even then, after being back at the new iPad for a couple minutes, I completely forgot about it. If you are looking for pixels, sure, you'll notice. If you're just using your device and thinking about other things, probably not so much. Reply
  • PeteH - Wednesday, March 28, 2012 - link

    Eh, I think it depends on what application you use the iPad for. Web browsing and Tweeting? You're probably right, you wouldn't notice the difference in displays. But if you use it to view images I could see it being a big deal. Reply
  • zorxd - Wednesday, March 28, 2012 - link

    I am pretty sure extra resolution is more noticeable when reading text than when looking at images Reply
  • PeteH - Wednesday, March 28, 2012 - link

    I didn't mean "notice" as in you couldn't tell the difference, just that the difference wouldn't be something that you would constantly be aware of if you were simply web browsing.

    If you were reading an e-book? Absolutely, but if that's your only use case I'd get a Kindle and save the money.

    Regularly viewing quality images is something that can't be done on an e-ink reader, but for which the improved display would make a huge difference.
    Reply
  • Sabresiberian - Thursday, March 29, 2012 - link

    I would say this is a perfect example of why it's better to use "I"" statements than say "YOU won't notice, YOU won't care, there isn't that much difference" - those kinds of statements. "I didn't notice much of a difference, it wasn't a big change in MY experience. . .)

    Displays can very very personal in experience, and things that bug the heck out of me may not be a problem to someone else. For example, a pixel pitch of around .270mm is just too big for me, in a monitor, and it bugs me. Always.

    Frame rates are a good example of something I'm not consciously aware of all the time, but I can sure tell the difference on some level, and some displays are more effected than others. There are extra factors in LCD screens that can make the problem worse for some of us - others don't notice so much, or it's just not a problem for them.

    One thing I believe, is that as more people use really better screens, they'll understand more why some of us call for them every chance we get.

    ;)
    Reply
  • darkcrayon - Wednesday, March 28, 2012 - link

    I can *immediately* notice the difference in web browsing, which is primarily focused on reading text... Reply
  • tipoo - Wednesday, March 28, 2012 - link

    I found it a noticeable difference, just not neuron melting like some reviews led me to think. For 100 or more less I'd still be plenty happy with an iPad 2, especially given the CPU and battery life performance are about the same. Reply
  • MobiusStrip - Thursday, March 29, 2012 - link

    Unfortunately the iPad 2's camera is a disgrace. It should've had the iPhone 4 camera, which was already out by that time. Reply
  • repoman27 - Thursday, March 29, 2012 - link

    The iPad 2 was also thinner than the iPhone 4. Now that it is the same width, it has the same camera. It's not really Apple's style to add thickness to a device just to support one feature that isn't heavily used anyway (tablets are not a very good form factor for a camera.) Reply
  • zanon - Wednesday, March 28, 2012 - link

    Human vision varies significantly from person to person, as do use patterns for machines. Someone who is more near sighted or simply has better vision in general, and/or uses their system at a closer distance, may see a truly dramatic change. To take my personal example, I have excellent color vision and am also near sighted, and tend to hold my devices relatively close (or use glasses at my machine). I can see the pixels on the iPhone 4 screens (326 ppi) if I focus a bit, and for the older screens (or old iPads) they're massively pixelated to me (not that that made them useless). The High DPI screens are a night/day difference personally, making all types of reading in particular (be it on a terminal session, the web, PDF manuals, ebooks, or whatever) massively more functional (and everything else more beautiful).

    But that's just me, and is that awesome? No, it's kind of meh, I'd love it if I didn't need glasses to use my desktop without being hunched over the keyboard to drive. But understand that you'll see raves about the screen that are completely justified, just not for you. 20/20 vision puts the critical distance around 13" I think, but in the end everyone will need to take a look for themselves.
    Reply

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