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3/21/2012
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Why The iPad 3 Regressed In Battery Life

Apple's new iPad is pushing technology boundaries to the limit with its ultra high-resolution screen. The result is some uncomfortable trade-offs in heat and power consumption.

Editor's note: The final paragraph of this article contains an update to the recommended external battery charger.

When Matt Drudge's headline about the iPad is "IT'S HOT", Apple has a small public relations crisis on its hands. The complaints about the third generation of iPads have spilled beyond the confines of geeky forums into mainstream media. From complaints about an uncomfortably hot slab of aluminum at 116 degrees Fahrenheit to the added thickness and weight and the much longer battery charging times, the new iPad seems to be enjoying a much shorter media honeymoon than usual for an Apple product.

In fairness to Apple, it was faced with the very difficult engineering task of integrating the highest resolution display on any notebook or tablet computer ever produced. To achieve the mind-boggling quad-XGA resolution of 2048 by 1536 pixels using the display technology available today, Apple had to more than double the power draw of the LED backlight that lights up the iPad screen. According to DisplayMate, Apple had to bump up the backlight power draw from 2.7 watts on the iPad 2 to 7 watts on the new iPad.

As DisplayMate explains it, that huge bump in power consumption in the LED backlight was caused by the use of amorphous silicon type LCD panels whose transistors block out more light when pixel density increases. The iPhone 4 in contrast has even higher pixel density--but its use of low temperature polysilicon (LTPS) technology makes the iPhone 4 more than twice as energy efficient per square inch to achieve the same brightness as the new iPad. The problem is that LTPS technology is expensive and would not have been practical for a screen as big as the new iPad's. A new display technology called indium gallium zinc oxide (IGZO) has the benefit of better energy efficiency at a competitive price, but IGZO isn't ready for mass production.

My initial guess was that fault lay with the Apple A5X CPU and the PowerVR SGX 543MP4 quad-core GPU needed to render all those new pixels, but the culprit seems to be primarily the backlight. And since no one's conducted 3D gaming battery tests yet, it remains to be seen how much worse things can get.

In other types of tests conducted by various tech publications, the new iPad consistently performs more poorly than the iPad 2. Anandtech, for instance, found that the new iPad draws 4.58 watts while surfing the Web over Wi-Fi while the iPad 2 draws a mere 2.48 watts. DisplayMate found that the new iPad at maximum brightness sitting idle draws 7.32 watts. The iPad 2? Only 3.47 watts. CNET found that the iPad 2 draws 1.76 watts at 150 candelas per square meter (cd/m2) brightness for 720p video playback. The new iPad draws 3.32 watts. These results show that there is approximately a doubling of power consumption, yet the new iPad's battery increased in size only 70%, from 25 watt hours to 42.5 watt hours.

The new iPad's ultra-high-rez push seems to run counter to Apple's form-over-function design philosophy. The bleeding-edge screen has inflicted tradeoffs in usability: the thicker and heavier chassis, much longer charge times, hotter surface temperatures, and shorter battery life. For photographers who crave higher resolution and higher color gamut, the new iPad is a must have. For everyone else craving an iPad, the decision is more difficult.

If you can't or won't wait for the next generation of ultra-high-resolution iPads with better energy efficiency, you might want to stock up on a few 37 watt hour battery packs at $55 apiece so you won't be tied to a wall socket. These battery packs will charge your smartphone and any other USB device you might have as well. [Update: It seems the Hyperion product linked to above does not support the new iPad after all. It claims to provide the required 1 amp, but only supplies 1/2. In fact, it seems that 2 amps is the effective minimum requirement for charging a third generation iPad. For a useful alternative, consider this no-name model which costs $69.99, but has several good reviews on Amazon.]

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