I have a Tom Tom 25. Why does it shut off/close down after I have been driving for some time although, it is connected to the car through its leads and jacking plug point, which are the original ones when purchased. When I turn it back on it states battery charging and shuts off again after a few minutes. I do not use it regularly. Does it need to be connected to a mains outlet in order to charge and bost the battery up and is there not sufficient power from the car to keep it maintained? I'd appreciate and help, advice and assistance in this matter.