I could calibrate everything this morning… 
Now the problem is an alert: low voltage in the board. I was going to use the Voltage and current sensing steps in the docs section, but I got a bigger power module and I am not sure which option I need to choose in the APM to read voltage. I am using a PM2.5.2 APM2.6 Pixhawk Power Module cable V1.0 Output BEC 3A W/XT60
Max input voltage: 30V.
Max current sensing: 90A.
Voltage and current measurement configured for 5V ADC.
Switching regulator outputs 5.3V and 3A max.
6P molex cable plugs directly to APM/Arduflyer 2.5’s ‘PM’ connector.