Battery level measurement (for Solar Power; DFR0559)

Dear All,

I am exploring a solar powered System that can measure different variables (Soil Moisture, Temperature,…). Therefore I have a nice Solar Power Manger from dfrobot.(Solar_Power_Manager_5V_SKU__DFR0559-DFRobot)

The wiki above shares a schematic how to measure the battery level of the LiPo Battery. However if I apply this to the NodeMCU I only get 5V all the time, although if I measure with Voltmeter, it’s the actual Battery level of the 3.7V LiPo.
I also replicated the schematic using a Arduino UNO and there the voltage is correct and aligned with the voltmeter.
What’s wrong here ? I assume the NodeMCU Analog Pin A1 is somehow measuring the 5V output as this is the boosted voltage (and kept constant). Or the analog-digital conversion of this port to 0-1023 is wrong. Any suggestions?

Your help would be very much appreciated.