Laptop plugged in and shuts down immediately when battery drops out

So I have a Dell Precision M4600 running Windows 7.  Whenever its plugged into the wall or docking station, if the battery drops out, it shuts down immediately as if I don't have it plugged into the wall.  Windows does tell me that its plugged in.  The battery charges fine as I have unplugged the laptop and used it off the battery.  So those are indicators that it is receiving power through the plug. 

So why should it power off if the battery gets disconnected?

Yes the battery is loose and right now I have duct tape holding it in.