Putting a phone in a cage will drain the battery fast if it's on as it takes much more power to try an find a signal to lock on to vs being locked on.
The designers have stopped this as well. Used to be that if you forgot to turn off cellular service on your phone on an airplane on a long flight, battery would be depleted when you landed as it kept trying to establish connection. Now it doesn't do that anymore. I believe that they got smart and plugged the hole. Battery management is a huge area of focus for phone designers as the more stuff they make the phone do, the worse the battery life. Battery technology only moves so fast