What is the electrical gismo mounted in the drivers side battery box, flat and round mounted flush with the bottom of the box?

 

I think it's a temperature sensor.

 

It's the battery temperature sensor that regulates the rate of charge.
Common problem develops when people use a spacer under the battery in cold climates. PCM thinks the battery is frozen and cuts off charging.
Need to make sure the bottom of the battery is in contact with the sensor.

 

Thanks. I love this site, somebody always knows.