Has anybody replaced the 12v on RWD S?

[Enigma32]

I went through the hell of gutting most of the frunk to access the battery. I managed to finagle it out and the new one in. The 8mm nut that fastens the fusebox to the battery strp fell somewhere, but I figure that won't be bad to drive without and get a replacement somewhere. But the big problem is the nut where you fasten the HV charge line to the fuse box is now free spinning. Rather, I can turn it for a bit then it "skips". So now I can neither fully fasten it, nor remove it. Anybody know how that bolt sits in place on the underside? I'm assuming its a square or hex head with a cutout that holds it still and that cutout is now stripped. Any ideas how to remove it so I can try and replace the bolt and nut to finish the job? I suppose I can wedge something in under the nut so it doesn't wiggle around and if sparks aren't flying I can drive like that temporarily...