Apple confirms imprecise iPad battery meter, says it's by design

Nothing to see here, exec tells AllThingsD, about reports that indicator shows a fully-charged battery when it's at 90%

Apple today reacted to reports that the new iPad under-reports its battery status, saying a researcher's analysis was essentially correct but that that's how the tablet and its iOS software were designed.

Apple executive Michael Tchao told the AllThingsD blog -- operated by Dow Jones, the same firm that publishes the Wall Street Journal -- that the new iPad, like all devices powered by iOS, reports a fully-charged battery before it actually reaches 100%.

According to Tchao, Apple's vice president of marketing, the iPad, iPhone and iPod Touch all display "100%" on their battery indicators before they are completely charged.

The battery continues to charge until it is, in fact, at full, when it goes into a cycle of slight discharge-recharge-slight discharge until the device is unplugged.

Last week, Ray Soneira, president of DisplayMate Technologies, reported that when the iPad's battery meter first shows 100%, the tablet is actually charged only to 90% capacity. If a user disconnected the tablet from an outlet when the charge says 100%, he or she would be shortchanged of more than an hour of power.

Although Soneira never questioned that the iPad's charge monitoring generally worked -- like any mobile or portable device, the iPad oversees the process to insure its lithium-polymer battery is not overcharged, and thus at risk to overheating or swelling -- he asserted that there was "something wrong with the battery charge mathematical model" that resulted in the inaccurate charge status.

Today, Soneira made note of Apple's acknowledgement that the iPad doesn't always report the true battery status.

"It's not the full admission that I would have liked, but it is actually more than I expected Apple would admit to," Soneira said in an email on Tuesday.

Tchao also denied that Apple has told users not to let the iPad charge after the meter reads 100%. That idea surfaced last week after CNBC reporter Jon Fortt said the company had said that charging above the 100% mark could damage the battery's longevity.

"That circuitry is designed so you can keep your device plugged in as long as you would like," Tchao told AllThingsD today. "It's a great feature that's always been in iOS."

Apple has never given such dire advice on its website, where the company offers battery longevity and charging guidance. A recommendation like that would also run counter to the long-standing practice of leaving portable devices unattended while charging.

Soneira was unable to immediately confirm Tchoa's claim that iOS devices cycle between discharge and recharge as their batteries near 100% capacity, but suspected that was the case. He also stood by his earlier analysis.

"If the iPad has cell and Wi-Fi and background tasks running, then I agree with Apple that it will cycle down and up," he said today. "[But] my lab tests were in Airplane Mode so that did not happen and I measured the true battery state."

Tchao also told AllThingsD that the decision not to constantly update the battery indicator near the end of the charging process was intended to minimize distractions and user confusion.

If that's the case, Apple failed, said Soneira.

"My essential point is simply that if the new iPad is fully charged overnight, then my tests show it will run 11.6 hours, which is 1.2 hours longer than if it just charged to 100% [on the meter], or 10.4 hours," said Soneira. "This will matter to some users."

Apple did not immediately reply to additional questions and a request to confirm Tchoa's statements to AllThingsD.

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, on Google+ or subscribe to Gregg's RSS feed . His email address is

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