It would depend on what it is connected to when you are seeing this. While connected to the USB port of a computer, many cannot provide the necessary power to charge the device, but it does supply some, and the iPad will charge a little bit. However, when it is connected to the power adapter that comes with the iPad and plugged into the wall, you should see it charging just fine.
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IPad says not charging
3 replies
Why does my I pad say "not charging" and still charges