Four of us walked into the hills behind Sa Pa with two phones and no paper map.
The application worked perfectly for three hours.
Then the disappeared, and the map on the screen became a square.
We had not the area for use without a , which takes one minute at home.
A farmer pointed us towards a that took two hours instead of forty minutes.
Nobody was in danger, and everybody was cold and hungry by the end.
Now I download the map before every trip and take a small paper one as well.
A battery pack sits in my bag next to the water bottle.
I also send our to one person who stays at home.
None of that is complicated; it only has to be done before the goes, not after.