In general, the way devices will handle this is to only draw 100 mA
> (which is typically enough to run, but not to charge a battery),
> link up, and once the driver is installed, ask the driver for
> permission, then switch up to the 500 mA (or higher in many cases) > mode.
Aha!
This seems to explain why the Motorola RAZR V3 can ONLY charge its battery on a PC USB cable if the cell phone is turned on with enough power to run the cell phone.
If the battery is so low that the cell phone can't "ask for permission", then the usb cable to the PC won't charge the phone.
There must be enough energy left in the battery to power up the phone so that the phone can ask for permission.