My understanding is that USB's don't push enough current. You need 2 Amps I think for that tablet to charge properly. I also believe it is "trickle charging". If you leave it and don't turn it on, it'll charge in a few days....
You'll probably notice some car chargers won't charge it either. Most car chargers push 500mA to 700mA. You need about 2000mA.
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