I'd like to know this too. I can tell you anecdotally that 4G (LTE at least) is a major battery drain if you have very weak 1-bar signal. I work in a basement and my phone is dead by 5pm unless I remember to turn on airplane mode.
You would do well to enable Wi-Fi calling in that circumstance if your provider offers the service. I had a misconception that that service was somehow inferior to getting a “real” connection to the cell network—not so. The cell network does not care how you access it, and more-or-less treats RATs (Radio Access Technolgies) as interchangeable.
