Many users commenting on the issue are careful to characterize the temperature of their new iPad as "warm" rather than "hot," and say the temperature won't affect their use or enjoyment of the device.
Some however insist the device is too hot to use comfortably. "The iPad 3 wasn't hot, but warm enough to be uncomfortable," said one person posting to Apple's forum. "That plus the extra weight made it not worth the new display to me, as awesome as it is."
Others are careful to phrase their acknowledgement of the issue in a way that doesn't reflect poorly upon Apple': "Yes, it's warmer than the previous iPads," said another person posting to Apple's forum. "But, what would anyone expect with so much going on in there? It has spectacular graphics, is faster, and has a huge battery. Any form of computer runs hotter when it is doing more."
[ Want to see what the iPad battery looks like? Click on New iPad Teardown: Inside Apple's Tablet. ]
A visit to the Apple Store at the Stownstown shopping center in San Francisco, Calif., on Monday confirmed that the new iPad does indeed get pleasantly warm when left on for prolonged periods, more so than the iPad 2. But Apple's tablet is not so warm that it could be used as a portable grill. (Note to app developers: Apple probably is not going to approve that hand-warmer app you just realized you could make.)
A staff member acknowledged that the new iPad can heat up, particularly following the use of applications that tax the processor, like games with high-quality graphics. But it's not going to burn your hand, I was told.
To some extent, such complaints can be expected: Product upgrades often prompt objections from those who preferred the old version. And recent Apple products, notably the iPhone 4 and the iPhone 4S, were accompanied by fretting about antenna quality and rapid battery draining. What's more, online forums are complaint magnets, while the silent, satisfied majority seldom weighs in.
It may be that Apple's iPad is operating as expected: With more powerful processing and network hardware in its new iPad, Apple planned for greater power drain with a larger battery, and that battery just happens to run warmer than the battery in the less powerful iPad 2.
It may be that Apple's latest mobile operating system, iOS 5.1, has inefficiencies or bugs that run apps in a way that tax the iPad's hardware unnecessarily and that a future iOS revision will help the iPad run cooler.
Or it may be that the iPad is not designed optimally for certain applications, like graphically intensive games.
Vincent Battaglia, program manager of the Advanced Energy Technologies Department in the Environmental Energy Technologies Division of the U.S. Department of Energy's Lawrence Berkeley National Laboratory, was careful to note that he has not evaluated the iPad's battery. But, he said, in general, the batteries used in mobile devices come with some design trade-offs.
"The problem is everyone wants these devices to last as long as possible before recharging," he said.
Batteries are designed for a certain rate of power consumption, he explained, and demanding energy at a faster rate increases electrical resistance, which causes heat.
"[Apple] may have packed in too much energy," Battaglia speculated, "or maybe the average draw is higher than what was designed for."
Computers, he said, can reach 55 Celsius (131 Fahrenheit) inside, which is why they have fans.
Battaglia noted that most of the research in lithium ion batteries at the moment focuses on longevity rather than higher conductivity--necessary to put power out at a faster rate. Almost all the oxides out there we know of, he said, have the theoretical limit of 280 milliamp-hours per gram. State of the art batteries are performing at 160 to 180 milliamp-hours per gram, he said, and beyond that, the material collapses.
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