If you leave your phone on and put it in a faraday cage, the battery will drain at the maximum rate as the phone goes into "find a tower" mode which is basicall

If you leave your phone on and put it in a faraday cage, the battery will drain at the maximum rate as the phone goes into "find a tower" mode which is basically to broadcast at maximum power over and over trying to make contact with any towers that might be within its maximum range.