The solution to this seems to be to purchase one of the very popular phones -- a Samsung Galaxy or an iPhone being the two sure bets I'm aware of -- and adding

The solution to this seems to be to purchase one of the very popular phones -- a Samsung Galaxy or an iPhone being the two sure bets I'm aware of -- and adding one of the cases that includes an integrated supplemental battery. Pricey and somewhat bulky, but it works. Plus, if the battery in the case goes, you can replace it. My friend had a case for her S6 from Mo-something-or-other, that had a "lifetime" warranty, and when the case battery became borked, she did indeed get a warranty replacement relatively painlessly -- though she did have to do it via mail with Mo-whatever, even though she purchased the case from one of her carrier's bricks and mortar stores. This was a disappointment for me with my Nexux 5X; when the battery seemed to be coming up a bit "short", I found no source for a case having an integrated supplemental battery.