The iPad 2,4 Review: 32nm Brings Better Battery Life
by Anand Lal Shimpi on May 4, 2012 12:50 AM ESTSignificant Battery Life Improvements
We'll start with the latest iteration of our WiFi web browsing test. With some additional logic to defeat overly aggressive browser caching, this test cycles through dozens of web pages, pausing on each one to simulate reading time before moving onto the next one. Display brightness is kept constant at 200 nits while the test runs. Results are reported in hours of battery life before the tablet dies.
Most web browsing tests end up being significantly display limited, as in the display dominates most of the power draw. That being the case, the fact that we see a 15.8% increase in battery life from the new 32nm HK+MG SoC alone is very significant. Apple is very conservative internally about revising battery life ratings so it's no surprise that we don't see a change in the specs on the iPad 2, especially considering that so many units out there on the market are still older iPad 2,1 models.
The increase in battery life here is almost certainly due to lower leakage at idle and better active power as well. This is a real improvement.
Things get even better when we stress the real power hog on the SoC: Imagination Technologies' PowerVR SGX 543MP2 GPU. Taking up more area on the die than the dual Cortex A9 cores, the 543MP2 is really stressed during 3D gaming. What better way to measure the impact of the new 32nm SoC on battery life than with one of the most stressful 3D games out for iOS today: Infinity Blade 2.
Here we're looping through the same scene until the battery dies, once again at normalized brightness.
The 3rd generation iPad obviously doesn't do as well as the iPad 2 here, as it not only has a more power hungry GPU but it's also rendering the scene at a higher resolution (and driving a higher resolution panel). What's most impressive however is just how much better the iPad 2,4 does here: a 29% increase in battery life over the original iPad 2,1.
Riptide GP, a less stressful title, shows us similar results:
Finally we have our brand new video playback test. Here we've got a copy of the last Harry Potter movie with the credits stripped out (1:58:00 running time), transcoded to a 720p High Profile H.264 video with a 4Mbps average bit rate, playing back in a loop until the battery dies.
The iPad 2 holds a 19% advantage over the 3rd generation iPad (once again for obvious reasons), however the iPad 2,4 absolutely dominates with an 18% increase in battery life. At 15.7 hours this is an insane amount of battery life from a single charge. Granted end users will see lower numbers if you watch at higher brightness settings (200 nits on our test panel was around 40% brightness), but the advantage from the new iPad should still remain just as significant.
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dagamer34 - Friday, May 4, 2012 - link
It's kind of a shame that Samsung wasn't ready to product a 32nm A5X for the new iPad. While it's obvious that most of the battery life "issues" come from the amount of power the backlight consumes, a cooler running SoC would have been much appreciated.PeteH - Friday, May 4, 2012 - link
I doubt Apple would risk an entirely new SoC on an unproven process. If the 32nm A5 had been delayed because of process issues they could just keep manufacturing 45nm A5s and shipping iPad 2s. If a 32nm A5X is delayed, you slip the iPad 3.Samus - Friday, May 4, 2012 - link
dagamer34, the backlighting in the new iPad consumes the same amount as any other screen in any other iPad. I assume what you are trying to say is the screen is where most power consumption is used, which is correct, and the case with almost all mobile devices.The new iPad does need a die shrink, though, that's for sure. The GPU portion of the A5X consumes around 30% of the battery alone when driving full resolution graphics, which is why it has 30% less battery life than the iPad 2.
sigmatau - Friday, May 4, 2012 - link
That didn't make much sense. The iPad 3 also has a battery that's almost double the iPad 2.j2ozone - Friday, May 4, 2012 - link
The display has 4x as many pixels > which means it has 4x as much pixel wiring > which absorbs 4x as much of the backlight as older ipad display wiring > which means the backlight has to be brighter > which uses more power.mbzastava - Friday, May 4, 2012 - link
It is not the backlight that is making the huge difference in power draw. it is the quad-core gpu that is working 4 times harder than the dual-core gpu it replaced. all backlighting is done via edge-lighting, and the delta in power consumption to step up to a marginally brighter output is negligible considering the doubling of the battery capacity (doubly especial since LEDs are already pretty efficient). If you have ever taken apart laptop LCD screens you would understand.frostyfiredude - Saturday, May 5, 2012 - link
There is a more beefy backlight for the reason ozone said, go look at the review of the 3rd gen iPad and you'll see how large an effect bumping up the brightness causes compared to in previous iPads.Another way to see this is by looking at the numbers in this review where power use between the iPad 3,1 2,1 and 2,4 are compared. In H.264 playback the GPU and CPU are both doing essentially nothing so it isolates the screen fairly effectively. At the same brightness iPad 3,1 uses 4.9W, iPad 2,1 uses 2.4W and iPad 2,4 uses 2.2W. This shows that the display uses around 2.5W more power at the chosen brightness level. Looking at the same chart the GPU appears to be pulling about 2W extra (assuming moonbat works the CPU as hard as infinity blade 2).
Steelbom - Friday, May 4, 2012 - link
The iPad 3's display does actually consume a lot more power than the iPad 2's display, coming in at 7 watts per hour compared to only 2.7 watts per hour, both at max brightness.I'd say the A5 uses at most 3w when under load, and I'd give the A5X about 4w.
http://www.displaymate.com/iPad_ShootOut_1.htm
(Scroll to the bottom and then up until you find the power consumption graphics.)
victorengel - Monday, July 16, 2012 - link
Something is wrong. Your units don't make any sense. Perhaps you meant watts rather than watts per hour?lolstebbo - Friday, May 4, 2012 - link
I think you can tell if it's a 2,4 or not: presumably, only the 2,4 models would have the iCloud logo on the box.