I am completely mystified by how my phone appears to be violating the laws of physics. Anyone who can figure this out deserves the title of 'Sherlock Holmes of Android'. Here goes: On my desk I have a T-Mobile MyTouch 4G, a USB cable for the MyTouch, and an external battery charger (EVO PowerBank 5000mAh, max 1000mA). I plug the phone into the external battery using the usb cable and turn on the phone and the external battery. The phone battery does NOT charge. Then, I plug the phone into a wall charger, a car charger, and my laptop, one at a time, using the same USB cable as before, and each time the phone DOES charge. Then, I take my phone, the USB cable, and the external battery to my local T-Mobile store. I plug my external battery into the display Galaxy 2S phone using the same USB cable as before, and the Galaxy 2S DOES charge. Finally, I have the T-mobile representative pull an approved T-mobile external battery off of the shelves and plug it into the Galaxy 2S. It charges. Then we plug the approved external battery into my MyTouch. It does not charge. How can that be? Isn't a power source a power source? What could possibly be preventing my phone from charging from an external battery that does not prevent it from charging anywhere else? The greatest of respect and admiration for anyone who comes up with a solution to this.