hear is the story. i left my interior hatch light on accidentally for a few days when i was out of town. so the battery was completely dead. i put in an old battery i had laying around. started up and worked great. its about 3 weeks later now. the car is now having charging problems it looks like. the battery gauge would jump all around. then it would stay low at all rpms and jump up from time to time and then go back down by the 2nd whitle line from the bottom. now the car doesnt move up at all and the gauge is at the last white line. is my battery bad? alternator? something else?