I have an original iPad mini that's having charging issues. I use the OEM charger (I have another one that is not OEM and this still happens) and after about 20 minutes of charging, I get the error message that "this accessory is not certified with this device" and it quits charging. If I unplug it, wait a few minutes and try again, I can get another round of juice, but it'll stop again after about 20 minutes. I have to wait. It won't immediately let me charge after unplugging/plugging. My ipad is a recent replacement after my other one had to be returned for warranty issues, but it worked fine at first. Does anyone know what could be causing this?