I recently removed the lower dash to change the cabin filter and found a hidden battery velcroed to the glove box.I know it is not OEM i am trying to figure why the previous owner had this installed.I have unplugged it for over a week and i don't find anything malfunctioning.Does anyone know what is the function for the plug that is under the dash passenger side?

 

Very weird.

 

Lo-jack batt backup?

 

Lo-jack is a good guess, Eric. I've seen home phone batteries that look a lot like that, so maybe some sort of transmitter/receiver is a good guess.