Something keeps draining the battery. It will start all day, take us all over town and start reliably during the day, but it goes dead overnight. We had the system tested, and we tested it ourselves. The alternator and battery are good. I get .2 ohms from the disconnected positive terminal to the chasis. I can't find a short anywhere. I took out the fuses one by one, and the resistance did not change. what can be wrong?