Battery voltage reading on WiFi LoRa32 v3.1 board

[sakiraykurt]

#include "Arduino.h"
#include <driver/adc.h>

#define PIN_VBAT ADC1_CHANNEL_1 // Battery Read
#define PIN_ADC_CTRL 37         // Battery Read Connection

uint8_t batterySampleIndex = 0;
const uint8_t batterySampleAmount = 20;
uint16_t batterySamples[batterySampleAmount];

void setup()
{
    // Serial
    Serial.begin(115200);

    // VBAT Connection
    pinMode(PIN_ADC_CTRL, OUTPUT);
    digitalWrite(PIN_ADC_CTRL, LOW);
    delay(10);

    for (size_t i = 0; i < batterySampleAmount; i++)
        batterySamples[i] = analogRead(PIN_VBAT);
}

void loop()
{
    uint16_t voltage = analogRead(PIN_VBAT);
    batterySamples[batterySampleIndex++] = voltage;
    batterySampleIndex %= batterySampleAmount;
    int total = 0;
    for (size_t i = 0; i < batterySampleAmount; i++)
        total += batterySamples[i];
    voltage = round((float)total / (float)batterySampleAmount);
    Serial.printf("\nvoltage %d\n", voltage);
    delay(1000);
}

Example code.

I can't able to read correct voltage values when the battery is connected only, the battery and the usb are connected and the usb is connected only.
I also tried multipliying with many conversion factors like (3.2, 3.9, 0,00402) to get true voltage.
Should I make my own voltage divider circuit with 2 resistors to read the battery level or is it enough to just write code?