What makes you think it's not charging? No led, no lightning bolt battery symbol, it says it isn't charging? This could be due to your cable. The connection may be weak and not supplying enough power to your device and the rate of consumption is higher than being provided preventing the device from charging. Simply replacing the cable, if this is the cause, should correct this issue. When the device is powered off it draws no power and anything gets charges the device.
VidJunky posted via the HTC M9