ESP32 voltage sensor connection problems TTGO T-display

Hi folks,
I really need some help to understand where is the mistake in my project.
I am connecting an ESP32 (TTGO T-display) with a voltage sensor to read a voltage change.

My project will be installed in the car, trying to sense the voltage of a gauge sender unit.
here attached the scheme of what I did.

The problem is that if I am sullying power to the ESP32 via USB, the voltage is correctly displayed, while if I plug the "battery" cable into the BATT port (attached to a 5v regulator) I see an "out of scale value".

Could it be that I'm somehow supplying to the board a double voltage? do you know what is the difference between power via BATT connection and via USB?