Drat. Either I stripped the threads in the negative terminal of the battery, or it was already stripped when I bought it. Since I've changed hundreds of batteries in airplanes and a few dozen in ground vehicles, I don't think it felt like I cross threaded it myself, but that won't fly well at the parts shop.
So... I can get a slightly wider self tapping screw/bolt, or jam/melt a .50 cal lead ball (from mah muzzleloader) into the hole, and drill/thread it back to stock. I'm really kinda thinking the first option, at least for a while. I'm gonna have to gut the engine compartment at some point anyway, and when I do that, I'll be after a better battery anyway.
Drat again... when I was distracted by the boogered terminal, I forgot to re-attach the 12v, so Earl wasn't charging just now when I drove to the truck stop and back. I'll re-connect that tomorrow when it's light out. My brain has been mush lately. I'm in school for network engineering, so maybe my brain's just full, and I'll stick with that excuse for now.
Driving Earl again, though... even with the window up... was pretty awesome. I was really missing having a truck handy.