Hi,
I should have mentioned that I have followed the documentation and I use value 17 in Ardupilot settings. However, like in the comments in post Problem with the ADC power module current input on Navio2 the multiplication factor should be set somewhere are range 100-150. Unfortunately the response is not linear over current range 1-5 Amps so fiddling with the coefficient is only a workaround.
I acquired my board three years ago but it has been unused until now. Perhaps the issue affected only those older boards (the other post is from 2016) if you know that the response with new boards is linear even at low current values, and coefficient around 17 is good to use.