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Like all modern computers, the iPad's charging circuitry automatically stops charging the battery and puts it on a trickle charge once it reaches 100 percent of its capacity. This maximum capacity decreases over time as the battery accumulates charge cycles, but it's quite gradual; iPads and most other modern Apple gear contain lithium batteries designed to retain 80 percent of their initial capacity after 1000 full charge/discharge cycles. That's 1000 times taking the iPad from 100 percent charged down to zero, or the equivalent.
It's worth restating that the iPad's charging circuitry automatically stops charging the battery when it senses the battery reached its maximum capacity. This is why you can leave your iPad plugged in overnight without worrying about the battery getting overcharged and exploding in a gooey, hot mess of chemicals and fire. The same is true of iPhones, iPods, and Macs -- once the battery is fully charged, the device throttles the charging circuits down to maintain a slow trickle charge that keeps the battery at or near 100 percent. Or, if you want to go with CNBC's dumb analogy, the glass is actually designed to be filled to the rim, but the juice dispenser is smart enough to stop filling it automatically when it gets to that point.
However, Dr. Soneira and CNBC both seem to think that the bug pertaining to the iPad's charging indicator means the iPad is getting overcharged. They both argue that the iPad's battery is actually at 100 percent of its charge capacity when it says so, and leaving the iPad plugged in after that 100 percent overcharges the battery and causes damage.
As evidence, Dr. Soneira notes that allowing the iPad to charge for additional time after it reads 100 percent charged gives the iPad an additional 1.2 hours of running time. His analysis correctly shows that the 11.6 hour runtime he got by "overcharging" the iPad's battery is likely in line with Apple's officially-stated 10-hour battery life. Apple has a history of being optimistic with its battery estimates for Macs and conservative with estimates for iOS devices, so the 10.4 hour runtime Dr. Soneira achieved when he stopped charging the iPad's battery when it said it was at 100 percent is right in line with what we already know: the iPad isn't actually fully charged when it says it is.
When Dr. Soneira and CNBC both leap to the conclusion that the iPad is overcharging and therefore damaging its own battery, however, they both get it wrong. "Apple has put forth a rather shocking reverse perspective that the on-screen battery indicator is instead the correct one," Soneira claims, and CNBC says "Apple is saying.. if you charge it more than [when the battery indicator reads 100%], you could actually harm the longevity of the battery."
"According to Apple the new iPad is configured to damage the longevity of its own battery if it isn't manually disconnected from the AC charger when the 100% indicator appears," Dr. Soneira says, without providing a link to a page proving that Apple actually made this claim. "Anyone that recharges their iPad unattended, especially overnight, will be doing this."
In a word: no. This statement demonstrates a fundamental misunderstanding of how modern lithium battery technology works.
We reached out to Apple for comment, but we haven't heard back. We don't expect to, because this is a non-issue. The iPad may be telling us tall tales about its charge state in the status bar, but it's not destroying its own battery.
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