LG X Power passed its tests and no longer a test unit to me. It is around till gets replaced but is worth a mention here.
I did leave it on all night by mistake after a solid day of use (I was off and LG X Power got used nonstop) and day began at 43% and there was enough time to plug in and bring it up tp 63% before I walked out the door. And now after an hour of train ride I get what? 50% which probably lasts longer than most devices. Other phones need a low power mode since screen resolution may be so high and battery capacity so limited they cannot do what LG X Power does every day. Power save mode stink but if the device has a low power mode which reduces screen sharpness and power use there may be hope after all.