int value = 0;
float voltage;
float perc;

void setup(){
  Serial.begin(9600);
  }

  void loop(){
    value = analogRead(A0);
      voltage = value * 5.0/1023;
        perc = map(voltage, 3.6, 4.2, 0, 100);
          Serial.print("Voltage= ");
            Serial.println(voltage);
              Serial.print("Battery level= ");
                Serial.print(perc);
                  Serial.println(" %");
                    delay(500);
                    }