I have been experiencing crackling noises over the speakers and GPS and radio cutting in and out. Also the idrive toggle will not have the same resistance when I go to use it right after starting the car. After driving all systems seem to come back. Battery was tested and voltage was 10. My mechanic (not a BMW tech) says the battery isn't holding a charge and needs to be replaced because of age. Can the problem be anything else like a short or something?