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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  • Ammaross - Wednesday, March 28, 2012 - link

    "It has the fastest and best of nearly every component inside and out."

    Except the CPU is the same as in the iPad2, and by far not the "best" by any stretch of the imagination. Hey, what's the problem though? I have this nice shiny new tower, loads of RAM, bluray, SSD, and terabytes of hard drive space. Oh, don't mind that Pentium D processor, it's "good enough," or you must be using it wrong.
    Reply
  • tipoo - Wednesday, March 28, 2012 - link

    What's better that's shipping today? Higher clocked A9s, or quad core ones like the T3? Either would mean less battery life, worse thermal issues, or higher costs. Krait isn't in a shipping product yet. Tegra 3's additional cores still have dubious benefit. These operating systems don't have true multitasking, you basically have one thing running at a time plus some background services like music, and even on desktops after YEARS few applications scale well past four cores outside of the professional space. The next iPad will be out before quad core on tablets becomes useful, that I assure you of. Reply
  • zorxd - Wednesday, March 28, 2012 - link

    I'd gladly trade GPU power for CPU power.
    That GPU is power hungry too, probably more than two extra A9 cores, and the benefit is even more dubious unless you are a hardcore tablet gamer.
    Reply
  • TheJian - Wednesday, March 28, 2012 - link

    LOL, the problem is you'll have to buy that new ipad to take advantage because YOURS doesn't have those cores now. Once apps become available that utilize these cores (trust me their coming, anyone making an app today knows they'll have at least quad cpu and gpu in their phones their programming for next year, heck end of this year), the tegra 3 won't need to be thrown away to multitask. Google just has to put out the next rev of android and these tegra3's etc should become even better (I say etc because everyone else has quad coming at 28nm).

    The writing is on the wall for single/dual. The quad race on phones/tables is moving FAR faster than it did on PC's. After win8 these things will start playing a lot more nicely with our current desktops. Imagine an Intel x86 based quad (hopefully) with someone else's graphics running the same stuff as your desktop without making you cringe over the performance hit.

    I'm not quite sure how you get to Tegra3 costing more, having higher thermals (umm, ipad 3 is hot, not tegra3). The die is less than 1/2 the size of A5x. Seems they could easily slap double the gpus and come out about even with QUAD cpu too. IF NV double the gpus what would the die size be? 162mm or smaller I'd say. They should have went 1920x1200 which would have made it faster than ipad 2 no matter what game etc you ran. Unfortunately the retina screen makes it slower (which is why apple isn't pushing TEGRA ZONE quality graphics in their games for the most part...Just blade?). They could have made this comparison a no brainer if they would have went 1920x1200. I'm still waiting to see how long these last running HOT for a lot of people. I'm not a fan of roasted nuts :) Too bad they didn't put it off for 3 months and die shrink it to at least 32nm or even 40nm would have helped the heat issue, upclock the cpu a bit to make up for 2 core etc. More options to even things out. Translation everything at xmas or later will be better...Just wait if you can no matter what you want. I'm salivating over a galaxy S2 but it's just not quite powerful enough until the shrinks for s3 etc.
    Reply
  • tipoo - Wednesday, March 28, 2012 - link

    I didn't say the Tegra 3 is more expensive or has higher thermals; I said the A5X, with higher clocked cores or more cores would be, and we all know Apple likes comfortable margins. Would I like a quad core A5X? Sure. Would I pay more for it? Nope. Would I switch for reduced battery life and an even hotter chip than what Apple already made? Nope. With the retina display, the choice to put more focus on the GPU made sense, with Android tablets resolution maybe Tegra 3 makes more sense, so you can stop attacking straw man arguments I never made. There are still only a handful of apps that won't run on the first iPad and that's two years old, "only" two cores won't hold you back for a while, plus iOS devs have less variation of specs to deal with so I'm sure compatibility with this iPad will be assured for at least two or three years. If I was buying one today, which I am not, I wouldn't be worried about that.

    Heck, even the 3GS runs most apps still and gets iOS updates.
    Reply
  • pickica - Monday, April 2, 2012 - link

    The New Ipad 2 is probably gonna have a dual A15, which means dual cores will stay. Reply
  • Peter_St - Monday, April 2, 2012 - link

    The problem here is that most people have no idea what they are talking about. It was just few years ago that we all used Dual Core CPUs on our Desktop Computers and we ran way more CPU load intensive applications, and now all of a sudden some marketing bonzo from HTC and Samsung is telling me that I need Quasd Core CPU for Tablets and mobile devices, and 2+ GB of RAM,
    If you really need that hardware to run your mobile OS, then I would recommend you to fire all your OS developers, get a new crew, and start from scratch...
    Reply
  • BSMonitor - Wednesday, March 28, 2012 - link

    If you were to run the same applications a tablet is designed to, then yes, your Pentium D would actually be overkill. Reply
  • PeteH - Wednesday, March 28, 2012 - link

    The point is made in the article is that it would be impossible provide the quad GPUs (necessary to handle that display) AND quad CPUs. Given you can only do one or the other, quad GPUs is the right choice. Reply
  • zorxd - Wednesday, March 28, 2012 - link

    was it also the right choice to NOT upgrade the GPU when going from the iPhone 3GS to iPhone 4? Reply

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