int battery_pin = A3;

    float battery_read()
    {
        //read battery voltage per %
        long sum = 0;          // sum of samples taken
        float voltage = 0.0;            // calculated voltage
        long battery_min = 0;  //minimum voltage of battery before shutdown
        long battery_max = 5000;  //maximum voltage of battery

        // collect 256 readings (256x oversampling)
        for (int i = 0; i < 256; i++)
        {
            sum += analogRead(battery_pin);
            delayMicroseconds(1000);
        }
        // map the oversampled range (1024 * 2^8) to 0-5000 (map uses integer math), then divide by 1000
        voltage = map(sum, 0, 262144L, battery_min, battery_max) / 1000.0;

        return voltage;
    }

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

    void loop()
    {
        Serial.print("Battery Level: ");
        Serial.println(battery_read(), 2);
        delay(1000);
    }