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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  • Jamezrp - Wednesday, March 28, 2012 - link

    Didn't want to cause Verizon too much trouble? Heh, very funny. I am amazed at how the iPad ends up being an amazingly good Wi-Fi hotspot. It almost seems like business users should opt to get an iPad for that function alone. I know plenty of people who would be happy to keep it in their bag, with the hotspot feature enabled constantly, while travelling about. Even for the price there is nothing even close that can compare.

    Plus, you know, you get the tablet too.
    Reply
  • supertwister - Wednesday, March 28, 2012 - link

    "It’s a quantum leap from the noisy, 0.7MP mess that was the iPad 2 camera."

    Interesting choice of word considering a quantum is the smallest possible division for a quantity...
    Reply
  • omion - Wednesday, March 28, 2012 - link

    Quantum leap:
    (n) an abrupt change, sudden increase, or dramatic advance

    The phrase comes from the ability of particles to make a sudden jump between two energy levels. It is a leap (of any amount) between two quantization levels, not a leap of the smallest possible amount.
    Reply
  • drwho9437 - Wednesday, March 28, 2012 - link

    A large fraction of the die doesn't seem to have a known use? Wondering what could be taking up all that area if not GPU, CPU and memory interfaces/caches... Most other I/O would have small footprints... Reply
  • tipoo - Wednesday, March 28, 2012 - link

    The 4S had a larger than usual die for its voice cancellation features that were needed to make Siri work well, the iPad does't have that but it does have voice dictation so some space is probably for that. Reply
  • PeteH - Wednesday, March 28, 2012 - link

    A big chunk of it is probably the ISP they talked about when the 4S debuted. Reply
  • Lucian Armasu - Wednesday, March 28, 2012 - link

    So this is how I assumed. The new iPad is in fact slower than the iPad 2, if games actually start using the 2048x1536 resolution for their apps, which everyone seems to be encouraging them to do. But once they do that the graphics will either look poorer, or they will be slower than they were on the old resolution, even on an iPad 2.

    Add that to the fact that apps are much bigger in size with the retina resolution, and the CPU is the same as last year. The new display might look great, but it's obvious that the new iPad is absolutely a step-back in terms of performance, whether it's GPU or CPU we're talking about. Hardly worth an upgrade, especially for iPad 2 owners.
    Reply
  • xype - Thursday, March 29, 2012 - link

    Blah blah blah performance blah not worth it.

    I don’t give a shit about theoretical performance that I might be getting if DNA folding software was available for tablets. I really, really give a shit about being able to read website and ebook text without my eyes straining after an hour.

    One would think that 10 years after "No wireless. Less space than a nomad. Lame." and Apple raking in millions and billions of profit, those Geek Metrics™ that people are so fond of here (nothing wrong with that, it’s interesting stuff!), would be recognized as completely and utterly worthless to the average population. But apparently not.

    The iPad was never ment to replace PCs and Consoles as a hardcore gaming device, and it was never ment as a render farm server replacement. It would be really nice if people realized that, at some point. In the next 5 years, perhaps.
    Reply
  • tipoo - Thursday, March 29, 2012 - link

    It seems a bit like the 3GS-4 transition, it used the same GPU despite higher resolution and so performed worse at native, although in this case the CPU is unchanged and the GPU is "only" 2x better for 4x the pixels. Developers got around that on the 4 by making games for the old resolution and using upscaling mode. I'd imagine they will do the same here once games hit the limits of the GPU at native. Games like Infinity Blade 2 also use separate resolutions for things like the menus vs shadows vs terrain textures. Reply
  • darkcrayon - Thursday, March 29, 2012 - link

    I guess if the only thing you bought an iPad for were games, and you could only consider a game to be worthwhile if it were drawn directly at 2048x1536, you'd have a point. But of course the new iPad could play games at the "iPad 2" resolution at much higher detail, or at a slightly resolution with the same detail, etc.

    It doesn't make sense to say it's a step backward in performance overall- it simply has the option to display much higher resolution graphics that the old model didn't have. The iPad 2 displays 2048 x 1536 text at "0 mhz" so to speak. It's not like you are losing anything by having the option of ultra high resolution if the type of game (or app) can use it within the hardware capabilities.
    Reply

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