Originally Posted by cordelli

I believe, though I'm not 100% sure, that the Nexus cable has a couple of pins shorted to allow it to charge at full power, and if those pins are not shorted, it will only charge at 500 ma, no matter how much power you are pushing into the cable.

So the only way to get the full charge is to get a cable with the data pins shorted, or make one on your own. Otherwise, the tablet will drop down to 500 ma, because it doesn't know what it's plugged into.

They may have changed that recently, but in the past it was the issue.

There's plenty of pages online showing you how to short the pins on a regular usb cable to get the device fooled.