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Those are surely the symptoms of battery failure. This is quite likely enough in a Magellan device that is over 2 years old.
Would you like instructions on replacing the battery, and where to get a replacement battery of the right type for your model of Magellan? If so, please tell me the model of your Magellan, and whether it is a RoadMate or some other model line name. "PF11" may be a serial # but means nothing to me in terms of model identification, which is needed for getting the right battery.