1. Key Fob Battery While your key fob can last for a long time, it is not indefinite and has a time limit. Normally, it is 8 years with a well-maintained car and key, but if you have been dropping the keys a little more than usual, you are lucky if it lasts for 4 years. When you changed the battery in your key fob, it stopped working due to broken contacts, misalignment of buttons, or because the transmitter needs to be reset. You can use the key fob to start your car if you have an Intelligent Key system. r4awk.