I have connected black to black and red to red pigtail from the battery tender to the 12v battery terminals still inside my Honda Accord 2007 V6 car. I had to cut a small gap on the rings to screw it to the battery terminals since I have ample space on the thread and I just had to squeeze them from the side. Question though since not sure if that’s grounded as well via the negative terminal? Please advice.

PS: My MB ML350 has a dedicated positive and ground terminal inside the hood unlike Honda Accord.