I have an HTC Windows phone (Verizon service) and the original charger (TC P900 US) will shut itself off after a period of time. It charges the phone while it's working. I don't have this issue with my spare chargers only the one that came with the phone. Is the charger designed to do that or might I have a defective charger? If I unplug it for a minute or so, it works again when I plug it back in. It won't start working again until after I unplug it for a short time, doesn't start again on its own. This doesn't affect the phone's operation other than using the battery when the charger shuts off.