2002 Buick Rendezvous - Won't start the second time

Yesterday, found a broken wire on the crankshaft position sensor. Repaired. Before putting everything
back together, I am checking wiring for another problem. Reading 8.2 volts between battery ground terminal and chasis, this was after removing the wire that connects from the battery ground terminal to the chasis. I was trying to find why I am getting a spark at the battery ground every time I am reconnecting the ground cable to battery ground. If I leave it connected for a couple of days, the battery goes down to 0 volts.New troubleshooting begins anew.

Thatā€™s expected if the battery neg post isnā€™t connected to the chassis. I expect the car doesnā€™t work very well in that condition. Running the engine without that cable connected could damage something, such as the alternator or computer.