FWIW, it's a myth that using your phone for navigation kills the batteries. I went for a 6-hour ride today, using the Ride with GPS app for navigation. When I got home, the battery was still at about 75%. This is with an iPhone 11 (so, new-ish), no power-saving measures enabled, screen mostly off.

The thing about RwGPS is that it's not like Google Maps, which recalculates your route on the fly if you go off-course. RwGPS is more like a smart cue sheet that helps you follow a planned route. It lets you know when you're off course (which takes no more than half a block to recognize), but it doesn't tell you how to get back on course, or recalculate your route.