One other big power savings with a phone is downloading the maps. Google lets you do that and so does RWGPS. It takes a few steps with either app. RWGPS suggests turning the phone to airplane or offline mode.

I have ridden with someone that uses rwgps for navigation, even on long rides. He has a power bank that's bigger than his phone. Not sure that's fully necessary, but the longest I have used rwgps for navigation was about 60 miles.