I dunno, if you can figure out how to do a bike tour, you should be able to figure out how to use offline maps on a smartphone. Isn't that hard. I'd rather put the $$ saved towards other more important gear. I mean even paper maps are enough to figure out where you're going.

Charging was never an issue on my tours. I kept a solar panel power bank on top of my handlebar bag, which charged my phone that sat right below it with maps open. My phone was at 100% when I was ready to setup camp, and half the tour I was camped somewhere with outlets I could use at night. I never had to worry about battery life, and that was using maps the entire time I rode, playing music to a bluetooth speaker, texting friends etc.