I tried it without the battery cover and it works normally. It is like the cover acting like a shield and reduces the signal. I drove with my car for about 10 kilometres having the GPS Test app running, it never lost signal, had always in view 10 - 14 satellites and in use more than 10. I will test it more to find the solution because when i put the battery cover back in place i don’t have gps as every 2 meters it looses the signal.

After some trial and error i found out that the pin that makes contact with the back cover and works as an antenna is the one which is at the top left corner as you look it from the back with the case open. I put a piece of aluminum foil at the contact point and now at last it works properly. Another idea which i didn’t try was to apply some solder with a soldering gun to make the contact point better. If you want to press the screen without opening it as it is mentioned before, you have to press the top right corner as you look it at the front side in order to force it to make good contact. I bought mine with a cracked screen and changed it myself, i didn’t test the gps before the repair and i tried to use it a long after i had fixed it and found out that there was some kind of problem. Also i applied three layers of adhesive tape on the vibrator motor because after i opened it it didn’t also touched the back cover as it should and it didn’t vibrate on touch. Now everything works fine, i think the problem is the poor design of the back cover and the way it makes contact with the internal parts.

Update: I compared it side by side with a Samsung J5 2016, Samsung had a lot stronger signal, locked instantly and always had more satellites in use. I ordered copper adhesive tape double side conductive and when i get it i will experiment if i can build an internal antenna in the back cover.

Anyway the gps is at least functional now and i can use it. Before it was not.