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I have a MacBook Pro with both Mac OS X Lion and Windows (under BootCamp) installed. While in Windows, I tried to charge my iPad 3 via the USB port. The iPad says "Not charging", but really, it does, just super slow (4-5% per hour). The reason for this is that the iPad requires 2.1 A of current, but a standard USB port provides 0.5 A.

However, if I switch to Mac OS X, the iPad states that it is charging and it does at a rate of about 10% per hour.

The only takeaway from this is that either OS X puts out more current on the USB port or that it recognizes the iPad and acts accordingly.

Can someone provide more information on what is actually happening?

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up vote 4 down vote accepted

Apple has a support article which covers this question nicely. They explain how an Apple device can request additional power when their operating system is running which allows the iPad and other higher-power peripherals to charge more quickly under certain conditions. They specifically state that a USB port will not provide more power than usual when Windows is booted through BootCamp.

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Yep. This is exactly what I was looking for. – AngryHacker Apr 18 '12 at 19:00

There is a solution. Asus makes an app called Ai Charger. I have used it before with mixed results, but mostly positive. It increases charge amps to osx levels in windows, it also enables charge while sleeping (ONLY if the device was plugged in when the computer was awake)

Its free obviously, and works on non Asus computers. I couldn't get it to work properly under parallels/vmware, but its not that big of a deal, cos you could just tell it to hook to osx and charge instead of the VM.

You can download Ai Charger here

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