A small external battery is a great idea. Something that will hold two full charges is only a few ounces and can be purchased for about $20.

I have purchased backcountry navigator but I'm currently using Alltrails. It is a bit more but it has a number of different maps and overlays for each area.
It also allows you to make custom topographic, satellite, and other maps you can download and print out in all the standard topo sizes.

I also use a free app called GPS essentials for my car waypoint in town or on the trail. I really like it because it has a great dashboard feature. I have setup my dashboard to include sunrise and sunset so I know how much longer to hike, moonrise, moon set, and moon phases to know how much ambient light I'll have at night. an electronic compass, my altitude and the GPS' accuracy.

Another great free app for wayfinding at night is Skymap. It is an old app but you can look for a specific star so it's a good way to find north or other directions if you have knowledge of constellations. With the search feature it's great on a cloudy night.

These three apps,a battery phone case and a map and compass are what I use on the trail.

As always, I'm just a user of the apps.