One to add to list- the sprint variant of the LG G8 Thinq..... It will connect to TMobile, but you lose all service until you connect back to a Sprint tower. I have one- bought it November of 2019 (it was NOT CHEAP).... Was having service issues and went to a Sprint/TMobile store and was told phone is incompatible…

Did this once with 4 "D" batteries but wired in a 12v zener diode to limit current and drop volts down about 0.7 to 5.3v. Never had a problem bulky but worked fine good for emergency use but with what the parts cost me I could have bought a good rechargable one.