Pixhawk 2 battery voltage has feedback problem under load

I have problems in debugging the pixhawk2. The battery voltage in the flight process that the power module feeds back to the ground station greatly differs from the actual measured battery voltage in the flight. For example, the voltage displayed on the MP and the external power of the aircraft before takeoff The display shows the same voltage. After the take-off, the external power indicator shows 24.7v, MP shows 22.5v, and the external battery indicator and MP show 25.3v before take-off. Who encountered this condition in the debugging process?
Firmware Version: 3.4.5-3.5.5
MP version: 1.3.48-1.3.55
The voltage value has been calibrated in the state that the aircraft has not been started. The difference between the MP display voltage and the actual measured value after the aircraft started increases with the current, and I use the voltage data of the power module in this aircraft circuit to fly another. In control, after this aircraft is started, the voltage value fed back from the power module read by another flight controller is the same as the actual measured value. What settings can I check for in this case?
The power module’s sensors have also tried to change, but the data obtained is more inaccurate.

Did you calibrate per steps shown in wiki? Also could be due to the precision of your external battery indicators? A voltage of 25.3v, for instance, is most likely inaccurate for a 6S battery whose maximum voltage is typically 25.2v a few seconds after it is fully charged, and less usually even after just a few minutes.

Also for high precision it’s best to use a hall effect current sensor as available with Mauch power modules.

Has been calibrated in accordance with the calibration method provided by Hex official, the battery voltage is confirmed with a multimeter, so the current problem makes me very confused, the two days of testing found a new problem, in the choice of the correct sensor type calibration Voltage, unlocked The load voltage after takeoff does not seem to follow the actual voltage completely, and it seems to simulate the battery voltage drop.