Sort of defeats the point

I've had the rechargable battery pack w/cable for a couple of months now. The advertising indicates that you can play while you charge, and I've had it in that configuration for about 15 hours of gameplay now, using the included cord to connect the Pack to the USB port on my Xbox 360. It seems that this would be plenty of time for the unit to charge, but the light remains red and each time I try to disconnect the cable from the battery pack, the controller goes dead. Basically, this has turned my wireless controller into a plug-in. Yay.