Once again the complexity of lithium battery charging causes confusion about 'overcharging' and potential battery damage.

New iPad battery charge confusion

Apple has defended the way that the third-generation iPad displays battery charge information following the discovery that the tablet reports the battery full while still charging the battery.

"I noticed that the power meter indicated that the iPad AC charger was still continuing to deliver close to the full 10 watt recharging power long after the screen indicator showed that the battery was 100% charged." said DisplayMate chief Ray Soneira.

Soneira noted that the time the iPad kept charging was over an hour if the tablet was powered off and over two hours if it was powered up. That said, Soneira pointed out that the iPad would keep running for over 10 hours – Apple’s stated run-top – if unplugged based on the "100% charged" indicator.

However if allowing the iPad to fully charge, running time was extended to 11.6 hours according to Soneira’s testing.

The issue was made less clear by Apple’s remark that the iPad battery could be damaged by continuing to charge after the battery indicated it was full, according to an Apple quote on CNBC helpfully dumbed down with a demonstration involving glasses of juice.

Understandably this resulted in a good deal of concern given how easy it is to leave a device connected to a computer overnight and so on. Likely the comment provided to CNBC was either an off-the-cuff remark or, as discussed later, simply misconstrued.

Apple later clarified to AllThingsD: "That circuitry is designed so you can keep your device plugged in as long as you would like," adding that it was a feature "that’s always been in iOS."

In fact it’s a feature that’s always been in any Lithium-based battery chemistry charging circuit in countless millions of devices well before Apple came to the market. If any device failed to stop charging such batteries then the result would be dangerous over heating and fires.

To look at Apple’s initial remark another way, it is actually true that charging lithium-chemistry batteries completely actually does somewhat reduce the life time of the battery in the long run.

Notebook manufacturers have had various ways of dealing with this including only charging to ninety something per cent, while informing the user of that, or offering the user the choice in battery management software such as Lenovo’s ThinkVantage Power Manager.

It seems Apple’s strategy is to charge the battery fully if plugged in, but tell the user the battery is fully charged somewhat near the optimum 90 per cent mark. Armed with this knowledge, third-generation iPad owners can make their own decision.

If they want the longest running time, leave the device plugged in. If they want the lowest long-term degradation of the battery then it’s better to unplug it when the indicator shows full.

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