I learned very early (I was 16) that a battery can have a short. Here is the story. I haven't run into it since but I have the knowledge if the symptoms appear again on another vehicle. Car: 1951 Studebaker 6 volt system. A friend left his lights on and the his battery was dead. I had jumper cables and thought I'd help him out. His car was 12 volt. At the time I did not know cars had different voltage systems (infrequent today). I hook up the cables and tries to start his car and it only clicks. Re-adjust cables. Still no go. I tell him sorry, I guess my cables are bad. That act of kindness cost me more money than the car was worth and the various mechanics that attempted to diagnose why when I shut down the Studebaker the Amp gauge would go all the way to "discharge" and drain the battery if I didn't unhook the cable. ALL of the mechanics, including a shop specializing in electrical problems, stated it was the voltage regulator. In all, 4 voltage regulators were put on the car and none of them solved the problem. Whenever I shut the car off I had to pop the hood and disconnect a battery cable. I finally saved up enough to buy another car, a 1959 Morris Minor (which is Positive to ground!!! but it is 12v). I sold the car for $60 to a classmate. One day he comes into school and says my dad and I fixed the electrical problems with the Studebaker. I was astonished and ask what was it. He said all we did is replace the battery and it hasn't been a problem since. When I jumped that car evidently I damaged the battery causing an internal short. Wow, who would have thought?