The GPS app in my cell phone doesn't use cell tower reception, it works like any other GPS off satellites.What I like about the cell phone GPS is it shows your location in landscape mode and when you open the app, it shows exactly where you are and it tracks you as you walk ..I carry a cell phone charger in my pack that is good for about 4 complete phone charges.But any GPS unit is a good thing to have with you when miles from the road.I'd suggest spending a few extra bucks for a good one.
Dave I use the Google Map app.....It's like a helicopter is flying right above your head videoing your movements.