New to touring but my phone (RedMi Note 3) has been working well as the GPS, map/route and logger so far.
Tested out for x2 brevets (235km each) and a 2 day short tour.
The battery on some of the new phones are rather large (4600-5000mAh).
On 13hrs cycling, my phone was down about 55%.

Logging app -Strava
Maps/route - Orux (which can work with downloaded maps w/o data)
Screen was on auto off after 5mins and I checked when I needed from the phone mount)


Adding on a 5000mAh or 10000mAh backup should suffice.

My few cents