Can anyone explain why after a certain amount of time the cigar lighter circuit appears to shut down? Im using it as a power port to charge cell phone. When i get in the car, start it and plug the charger into outlet, it charges. It stays charging for an undetermined amount of time, then shuts off. I pull out the charger, put cigar lighter in to check if its outlet or charger, cigar lighter doesnt heat. Arrive at destination, turn vehicle off. When i start car again, power is back to outlet. Not understanding.