New iPad's battery life matches Apple's claims, but iPad 2 lasts longer

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You can’t talk battery life without running battery tests. So that’s what Macworld Lab has been busy doing the past few days. Our results: The third-generation iPad lives up to Apple’s promise of a 10-hour battery life in some cases. But the iPad 2 outperformed the new tablet in our testing.

That’s a bit of surprise. When it unveiled the new iPad earlier this month, Apple said that battery life of the new model and its predecessor would be similar.

The setup

To test the iPad’s battery life, we took a fully charged iPad, connected it to our local Wi-Fi network and played back a movie in full screen mode until the battery died. We did this with two different brightness settings—full brightness and at a measured brightness of 150 cd/m^2. (That’s candela per square meter—a measurement of luminance.)

Battery tests take a long time and having to manually restart a movie each time it finishes can be a hassle. Luckily, 1963’s Cleopatra has a running time of over 4 hours and is available on iTunes, so I don’t have to watch over the iPad constantly while testing. (I will, however, take this opportunity to publicly request that Apple include a looping feature in the next version of iOS similar to that found in the company’s QuickTime player for OS X. Can’t hurt to ask, right?)

There’s been some debate lately over when a fully charged iPad is really a fully charged iPad. We’ll leave that issue for the folks at DisplayMate to grapple with. Our tests with a power meter showed the new iPad to start dropping its power draw when its battery life indicator got to 90 percent. It started dropping a little quicker between 95 percent and 100 percent, at which time our meter showed the iPad drawing 4 Watts and continuing to drop. Thirty-five minutes after hitting 100 percent, the iPad stopped drawing power.

To be on the safe side, we ran our battery tests after the iPad’s indicator stood at 100 percent for at least an hour.

The results

An iPad 2 with its screen at the brightest setting and with automatic brightness turned off and that’s also connected to a Wi-Fi network can play a movie at full screen for around 8 hours 30 minutes. The new iPad, using the same settings, stops after about 5 hours 40 minutes. That’s a pretty big difference for devices that are supposed to perform similarly.

One thing causing that difference in battery life is the difference in each device’s maximum screen brightness. Using a light meter, we found the max brightness on the iPad 2 to be 400 cd/m^2, compared to the new iPad’s 434 cd/m^2 measurement. The new iPad having four times more pixels than the iPad 2 would come into play here, too, of course.

Setting both devices to a lower screen brightness (as Apple does in its testing), we ran our test again. This time, the gap between the battery life test results narrowed, with the iPad 2 lasting 13 hours and 20 minutes and the new iPad lasting 10 hours and 10 minutes. That’s right in line with Apple’s battery life claims for the new iPad. What’s strange is that the iPad 2’s specifications state the same up-to-10 hour battery life, but our tests blew past that mark.

(It’s worth noting that Apple lists many battery tests that it runs in the fine print of its iPad specs page, but doesn’t specify the results for specific tests. It just provides that 10 hour result. We mention this to emphasize that our full brightness test produces results below that specification because it’s a very different test from what Apple is running.)

As a side note, we chose 150 cd/m^2, instead of just setting the brightness slider to the center so that we could compare results across a variety of tablets in future tests. While some of these devices offer bright displays, the Asus Transformer Prime and Toshiba Excite 10 LE  were the closest to the iPad’s luminance, measuring 365 cd/m^2. The Transformer Prime also offers a Super IPS mode for outdoor use that was much brighter than the new iPad, measuring 585cd/m^2. On the other hand, some tablets were pretty dim, even at their max brightness. Two tablets— one from ViewSonic and one from Pandigital—measured just 183 cd/m^2 at their brightest settings. 150 cd/m^2 seemed like a luminance level that even the most low-rent tablet could reach, and help to keep our testing consistent if we were to expand our testing to include more models. 

Have an iPad test you’d like to see Macworld Lab take on? Let us know in the comments.

[James Galbraith is Macworld Lab director.]

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