Help! Slow Battery Discharge

Everyone may have missed this and I may have misread but if you are on volts scale and you are reading 13 volts between your negative battery post and vehicle ground... you have a super ground problem and more like a very poor grnd, almost a open circiut. THAT needs to be resolved first.

I took it that he disconnected the ground, and put the voltmeter in between. It would be exactly an open circuit.