AVIC-F50BT positioning problem

[gabigrigore]

I know, this is  a very old model but maybe someone got into this and could help me. Here is the issue:

-  had a car battery failure after which my NAVI unit completely lost it orientation. It showed me miles away from my actual position and even more, while being parked the unit showed me I was moving (on the map screen);

- changed the gps antenna, same situation;

- did a factory reset and it "moved" me right in the center of Paris near the Arc de Triomphe (nice, but I wasn't there) 

Do not have any clue of what could have happened (besides the car battery going dead at some point) or how could I fix this. Did anyone encounter this kind of issue? Hope that someone could help me or at least point me towards something I could investigate further.

Thank you very much!