The nice thing about real GPSr units and things like Garmin watches is that they (depending on the model) can last a week to even weeks. E.g., if you use a GPSmap 67s for 8 hours per day, it lasts 3 weeks. In the older units you can even put AA batteries.

Cycling with a phone with the screen on and at full brightness (which is what you need on a sunny day), a phone will last a few hours at most. The magic of good GPSr units is that they use a transflective display, the sun is your 'backlight'. (And of course using something more akin to a microcontroller than a smartphone SoC.)

Also, in contrast to smartphones, these things are really rugged. Like last year I was cycling through the alps and accidentally dropped my GPSmap at ~30km/h (without a case or protection, who puts them on a GPSr?). It only has some scratches.