The board is designed to measure the battery level (voltage) with an uC's ADC. The on-board voltage divider must be parameterized (R1 and R2) according to the uC's max ADC input as well as the battery's voltage level. The battery voltage may be higher then the ADC's Vcc.
The circuit includes two MOSFETs to cut-off the voltage divider in order to not drain the battery when not in use. The uC must pull up EN to activate the voltage divider. If EN is left floating (e.g., the uC is turned off or in deep-sleep), the on-board pulldown resistor cuts of the voltage divider.License: CC-BY 4.0