I ran a Samsung S5 (?) like this many, many years ago and it was pretty cool but holy crap it was a beast. My jeans pockets started to stretch out from carrying it, and it was impossible to keep it in a jacket pocket at all.

I did similar with a galaxy S4 (third party battery w/special back case to accommodate the larger size). Worked nice but eventually the battery bulged.

The tradeoff with replaceable batteries is if when you swap the phone loses track of time until finding a cell tower. Fine if in range but a risk when hiking far away, and might also propagate the wrong time to your smartwatch.

It should be able to sync its clock slowly from the GPS signal. But I have no clue if the feature is actually implemented.

ulefone Armor. There are a couple other models that have a 13200mAh battery.

That's quite a line-up they have! I have a Elephone S3 pro, two day battery is really great when traveling, no worries. I'll strongly consider an Ulephone next..

Wow - what a great find! I'll be keeping track of that crew for my next phone! ('tho they don't seem to currently support Verizon network)

Yeah I had to go with a TMO reseller here and most of the time I am using calling-over-wifi to make up for TMO's spotty coverage.