Hello,
is it possible to measure voltage from 9V battery connected to Relay Module?
Thanks.
You can use voltage divider. Search for this term on this forum or google. Your battery 9 V needs to be divided (scaled down) so it wil not exceed 3V, which is the maximum voltage the analog inputs and ADC can measure. Otherwise you destroy the MCU GPIOs.
ADC pins are shown here
https://developers.hardwario.com/hardware/header-pinout