It’s my understanding that the phone cannot be tracked if the battery is removed. But......they could place a very small battery in the phone, on the circuit board that couldn’t be removed. Believe me, if they want to track you via this device or any other, like GPS or computers in your car, they can.
Could this be prevented by placing the phone into an all metal container?
You can prevent being tracked if you can restrict the phone’s antenna from sending and receiving signals. I have been told that you can buy “antistat” bags like those used to protect PCBs from ESD damage and put your phone in it to prevent being “followed.” It will take the phone some small period of time to find a cell tower though when you take it out to use.
“Believe me, if they want to track you via this device or any other, like GPS or computers in your car, they can.”
That’s why I always keep two cell phones registered in my name: one on my person, the other tied to a balloon which randomly floats around the neighborhood.