@aparcar On expansion Boards you can determine the battery voltage with the internal ADC on Pin P16. There is a voltage divider between the battery an P16, which divides the battery voltage by 2 or by 3.05, depending on the board. So you can use the ADC class (see https://docs.pycom.io/tutorials/all/adc/) with 11dB attenuation to read the input voltage and scale that by the divider. E.g. if the ADC tells 1.9V, and the divider is 2, the the battery voltage is 3.8V. Since the ADC is noisy, you may have to calculate an average over say 100 values taken. If you have an voltage meter, you should take that to obtain the proper scaling value.