Just to add to the excellent advice you got.
Turn on Map Caching in the DJI Go4 App and then come out to the main screen and tap the map so it is full screen. Then use your WiFi at home and cache all the Map data you will need for the area you are going to be flying in. Zoom and and pinch to make sure the phone gets a good amount of detail.
Then go into Airplane mode and shutdown any extra apps that might be running and your now ready to head out to the location.
Rob