Charging & Battery Life

The 4th gen iPad ships with a new 12W USB charger, a slight increase from the 10W model that shipped with all of the previous iPads. The new charger is no bigger than the previous version. Under max load the 12W charger will draw 13.57W at the wall. By comparison, the previous 10W model would pull a max of 12.44W. The 9% increase in power delivery does help shorten charge times a bit as it now only takes 5.69 hours for a complete charge (compared to ~6 with the old charger). It still takes a really long time to complete a full charge on the iPad, but without going to a larger power brick (or reducing the iPad's battery capacity) I don't see a simple solution here.

The iPad 4 is able to maintain charge equilibrium in the cases I tested, even under heavy load. With the 3rd generation iPad, if I ran Infinity Blade 2 while plugged in the total available battery charge would drop over time. On the 4th gen iPad, that no longer happens. I was able to maintain charge equilibrium even with the old 10W adapter on the iPad 4, pointing at overall power efficiency improvements rather than the new 12W adapter as the explanation for why this is now possible. It is possible that with fully loaded CPU and GPU cores that the new model wouldn't be able to maintain charge while powering the device, however I haven't encountered such a scenario yet.

Charge time isn't the only thing that improves with the 4th generation iPad. When Apple introduced the iPad 3, we saw a clear regression in battery life despite the much larger battery. I hate to sound like a broken record, but it's that same combination of power hungry display and big SoC that were responsible for the iPad 3's lower battery life. The iPad 4 doesn't ditch the display, but it does move to a 32nm LP HK+MG process for the SoC. Max power consumption should be higher thanks to the faster CPU/GPU cores, but given the same workload we should see a tangible improvement in battery life (similar to what we saw with the iPhone 5). We went through our standard suite of battery life tests to find out how things have changed since the iPad 3.

We've started running our new smartphone web browsing battery life test on tablets as well. If you missed its introduction in our iPhone 5 review, here's a bit about the new test:

We regularly load web pages at a fixed interval until the battery dies (all displays are calibrated to 200 nits as always). The differences between this test and our previous one boil down to the amount of network activity and CPU load.

On the network side, we've done a lot more to prevent aggressive browser caching of our web pages. Some caching is important otherwise you end up with a baseband/WiFi test, but it's clear what we had previously wasn't working. Brian made sure that despite the increased network load, the baseband/WiFi still have the opportunity to enter their idle states during the course of the benchmark.

We also increased CPU workload along two vectors: we decreased pause time between web page loads and we shifted to full desktop web pages, some of which are very js heavy. The end result is a CPU usage profile that mimics constant, heavy usage beyond just web browsing. Everything you do on your device ends up causing CPU usage peaks - opening applications, navigating around the OS and of course using apps themselves. Our 5th generation web browsing battery life test should map well to more types of mobile usage, not just idle content consumption of data from web pages.

AnandTech Tablet Bench 2013 - Web Browsing Battery Life

I no longer have a 45nm iPad 2 so forgive me for the incomplete dataset here (it's safe to say that the iPad 2 would at least equal the iPad 4 in battery life, if not exceed it), but battery life has improved appreciably since earlier this year. The iPad 4 lasts around 15% longer on a single charge compared to the 3rd gen iPad. It also edges out the iPad mini and Microsoft's Surface. There's a good advantage over the Nexus 10 as well, but all of these tablets have smaller batteries than the iPad 4..

We haven't yet rerun our new test on all of the tablets, so we turn to our older 4th gen test to provide some additional reference points:

Web Browsing Battery Life

Here we see that although Apple has improved things, the iPad 4 still remains behind the old iPad 2's battery life target. Also note that in a lighter CPU workload where the iPad 4's Swift cores aren't asleep for substantially longer than the iPad 3's Cortex A9s, the difference in battery life ends up being pretty minimal.

Our video playback test remains unchanged from previous tablet reviews. Here I'm playing a 4Mbps H.264 High Profile 720p rip I made of the Harry Potter 8 Blu-ray. The full movie plays through and is looped until the battery dies. Once again, the displays are calibrated to 200 nits:

Video Playback - H.264 720p High Profile (4Mbps)

Video playback battery life has finally surpassed that of the iPad 2. As we saw with our camera analysis, Apple did some work on the video encode hardware/software this generation - it's also possible that the decode path saw an improvement as well. The 32nm iPad 2,4 still remains the king of this test but that's a bit of an anomaly. It's rare that we see a pure die shrink with no added performance/features offered these days.

Our final cross-platform battery life test is the new GLBenchmark 2.5.1 Egypt HD test. Here we have a loop of the Egypt HD benchmark, capped to 30 fps, running on all of the devices with their screens calibrated to 200 nits.

AnandTech Tablet Bench 2013 - 3D Battery Life

The results here actually surprised me a bit, but they make sense when you think about them. Capped at 30 fps (like many heavy iOS games are) the 4th generation iPad actually has GPU performance to spare in the Egypt HD test (avg frame rate is 40 fps vs. 21 fps for the iPad 3). Despite the fact that the 4th gen iPad has a more power hungry GPU, that extra performance remains partially unused which, when combined with the more power efficient 32nm LP process, gives the new iPad a slight edge in gaming battery life. Note that this only applies to the situation where the workload is identical between the iPad 3 and 4. Earlier I showed that some games actually put the increased shader power to good use and increase image quality. In these cases where the iPad 4 is doing more physical work than the iPad 3, you may see no improvement in battery life or even a regression.

Thermals

The display and backlight in the 3rd generation iPad, combined with the large 45nm SoC, resulted in a tablet that got pretty warm under load. The 4th gen model doesn't do away with the display but it does move to silicon that can drive to low power sleep states quicker than before (given the same workload). The result is a tablet that has the potential to run a bit cooler depending on what you're doing with it.

Under full load however there's no getting around the fact that both the CPU and GPU cores are significantly faster than their predecessor. Running Infinity Blade 2 for an hour produced slightly higher surface temperatures on the iPad 4 vs. the iPad 3:

Thermal Comparison - iPad 3 vs. 4 - Infinity Blade 2 Loop (1hr)
Temperature Measurement Location Apple iPad 4 Apple iPad 3
Back of Tablet, Apple Logo 35.7C 34.4C
Back of Tablet, Hottest Point 39.9C 39.1C

The difference isn't huge and it's only noticeable if you switch between the two tablets, but there's no real improvement in worst case thermals. The iPad 4 remains one of the warmest tablets that I've used. It doesn't get uncomfortably hot but I would prefer a cooler running device. Unfortunately until we see a big improvement in display power consumption, I just don't know how that will be possible. The move to 20nm won't happen anytime soon.

Camera Quality & WiFi Performance Final Words
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  • Zink - Friday, December 07, 2012 - link

    HP Touchpad, oops. I live in that place RIM is from so I at least know how hard the PlayBook is failing. I wasn't trying to impact anything, just give my opinion on tablet display sizing. Reply
  • name99 - Sunday, December 09, 2012 - link

    Reviewers of Surface, for the most part, disagree. Reply
  • Death666Angel - Saturday, December 08, 2012 - link

    I use my tablet for playing games and watching my movies and shows when I'm on the train. Why are you telling me how to use my tablet? Reply
  • coder543 - Thursday, December 06, 2012 - link

    How is 4:3 just amazing for books and web browsing? You're not *used* to browsing in a different aspect ratio so you say it's worse. I owned the iPad 1 and used it for a full year as my primary compute device. I even typed a 10 or more page document on the touch screen. I'm very familiar with it. But I can tell you that browsing on a 16:10 display is a wondeful experience, and now that I've gotten past the 'weirdness', I see numerous advantages for it. Reply
  • headrush69 - Friday, December 07, 2012 - link

    What makes it's so wonderful?

    I find it funny because on the desktop with that same ratio, most web sites don't really seem to take advantage of the space and a full screen web browser is mostly wasted space.

    Maybe you go to site's optimizing for a mobile browser, but for me, I want the normal site on my tablet, I'm not on a small screen phone.
    Reply
  • eallan - Friday, December 07, 2012 - link

    Numerous advantages that you didn't list for what reason? Reply
  • name99 - Sunday, December 09, 2012 - link

    It IS wonderful if the primary material you read on your iPad is technical PDFs. Use a decent PDF reader to crop the margins, and you'll find that the content of pretty much all technical PDFs is at 4:3 ratio. Reply
  • darkcrayon - Thursday, December 06, 2012 - link

    Well, the 3rd gen iPad got dinged for not having enough GPU to drive its pixels... And here we have the Nexus 10 with even more pixels than the 3rd gen iPad, but even less GPU muscle. "Much better tablet"? Ehh not seeing it. And no points for "proper aspect ratio", it was even explained in the article that it's a tradeoff. If you can't see why it isn't helpful to have an aspect ratio that is close to that of typical paper documents, I don't know that to say... Reply
  • coder543 - Thursday, December 06, 2012 - link

    The Nexus 10's GPU muscle isn't properly represented by some benchmarks. It is honestly a cross between the iPad 3 and iPad 4 in terms of performance -- far from being worse than the iPad 3.

    What is the aspect ratio of legal pad? When you need paper that gets stuff done, you don't use anything resembling 4:3.
    Reply
  • KoolAidMan1 - Friday, December 07, 2012 - link

    A4 paper aspect ratio is about 4:3. I know because I read PDFs on my iPad for work all the time, fits perfectly in portrait mode.

    Landscape is ideal for web browsing and applications, the extra vertical space is always a good thing. Its the same reason my desktop and laptop monitors are 16:10, much better than 16:9.

    All 16:9 is good for is video, and I do way more than just that on my tablet.
    Reply

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