Rick, do you have any data on how many watts your phone will draw while navigating? I am sure that backlight (on or off, brightness setting) plays a big part of that. I am not asking about instantaneous data, more a question of how much power you would need in watt hours for a typical day of touring. And I am sure that the way you do that (bluetooth or other communication in use or not, on-line data or not, etc.) would also play a role. And yes, what you are doing that day would play a role too, are you keeping the screen visible for constant navigation or following a rail trail for hours that requires almost no screen time. I think an estimate of watt hours you would need each day on average would be an important part of figuring out what you need for charging capability.

And, if you are using a high power taillight like some people do, that could be another consideration. If you are charging up taillight(s) every day too, ... you get the idea.

Yesterday I did a 200k randonneuring event, one person used a phone for navigation, within a few hours after the start she had to plug into a powerbank to keep her phone running. I do not know if she started the day with a full charge or not, but most people that use their phone daily all day long try to charge up their phones overnight.

I suspect that phone navigation consumes a lot more power than dedicated GPS units. If so, that could dramatically increase your power needs for self sufficient touring.

My general recreation (non-cycling) GPS consumes about 7 to 8 watt hours in about 12 to 14 hours of use with backlight off. Full backlight, cut that time in half. It does not have any wireless capability, so that is an electric load I do not have to consider.