Datasheet

ENable pin

If you'd like to turn off the 3.3V regulator, you can do that with the EN(able) pin. Simply tie this pin to Ground and it will

disable the 3V regulator. The BAT and USB pins will still be powered

#define VBATPIN A7

float measuredvbat = analogRead(VBATPIN);

measuredvbat *= 2; // we divided by 2, so multiply back

measuredvbat *= 3.3; // Multiply by 3.3V, our reference voltage

measuredvbat /= 1024; // convert to voltage

Serial.print("VBat: " ); Serial.println(measuredvbat);