What in world is this for?

I know I should have taken a picture of it before I put the battery back in but I didn't really think of it....
Under the battery in the battery tray is what looks like a drain plug ... however it has a small metal ring placed around it and it is wired into the wires below the tray which looks like it goes to the headlights?
I'm just curious as to its purpose

battery temp sensor most likely. I dont know it's purpose but I have 2 other vehicles with them for some reason

I haven't actually seen it, but my 2001 is supposed to have a temperature sensor under the battery. It's purpose is to limit the charging current if the battery's temperature gets too high. Probably true for your year also.

It's definitely the battery temp sensor. Does as the name implies.

thanks