The first time I removed my battery I found the remnants of a nest and the plastic vacuum tube underneath the battery box chewed through. The little suckers love us for some reason.

The exact same thing happened to me several months ago when my battery went south. Having had the problem with other cars in the past I had been pretty dilligent about inspecting the engine bay for signs of rodent activity. Never thought to yank the battery for a look-see. Sneaky little varmints!!
I'm not 100% sold on the mothballs and cayenne pepper treatments either. I did those on a small Dodge pickup and noticed that the mice had at least tried to set up again weeks later, but with less residue and probably success.
I even found a nest under a spare tire wheel well in a trunk of one car.
"I hate those meeces to pieces!"