If it is the usb type then it should be standard 5 volts, if the gps required more current then the Motorola supplies it could overheat but I imagine a cell phone and gps device are pretty close in current requirements, you should be ok.
I do not know why, but most of the GPS units require a brand compatible charger even though they seem to fit the mini USB port just fine. Both my Magellan and my Tom Tom are the same way.
If it is the usb type then it should be standard 5 volts, if the gps required more current then the Motorola supplies it could overheat but I imagine a cell phone and gps device are pretty close in current requirements, you should be ok.
I do not know why, but most of the GPS units require a brand compatible charger even though they seem to fit the mini USB port just fine. Both my Magellan and my Tom Tom are the same way.