USB Connects to PC, Won't Charge

[soapdude]

The Nexus will connect to the computer, and the computer recognizes it, but it still says "Plug in charger" and the battery keeps going down. I have had to purchase a stand-alone battery charger but am interested to hear people's thoughts on why my battery won't charge. I have 3 batteries and none of them will charge in the phone. I have tried multiple cables and multiple USB ports and also straight AC. Nothing works. I have even replaced the USB port on the phone itself but it does the same thing.