Overkill BMS - broken SoC code

#include "bms.h"
#include "U8glib.h"
#include <Wire.h>
#include <Adafruit_SH1106.h>
#define BRIGHTNESS 0x01
#define BRIGHTNESSREG 0x81


#define OLED_RESET 4
Adafruit_SH1106 display(OLED_RESET);

OverkillSolarBms bms = OverkillSolarBms();
uint32_t last_update;


void setup() {
     display.begin(SH1106_SWITCHCAPVCC, 0x3C);

     display.display();
     display.clearDisplay();

    delay(500);

    Serial.begin(9600);

    while (!Serial) {  // Wait for the BMS serial port to initialize
    }

    last_update = millis();
    bms.begin(&Serial);

}

void loop() {
    bms.main_task();
    uint8_t soc = bms.get_state_of_charge();


    // Do something at 1 millisecond
    if (millis() - last_update >= 2500) {

          display.clearDisplay();
          display.setTextSize(4);
          display.setTextColor(WHITE);
          display.setCursor(0,0);

          display.print("State: ");
          display.print(soc, DEC);
          display.println("%");

          display.display();
          Wire.beginTransmission(0x3c);
          Wire.write(0x00);
          Wire.write(BRIGHTNESSREG);
          Wire.endTransmission();
          Wire.beginTransmission(0x3c);
          Wire.write(0x00);
          Wire.write(BRIGHTNESS);
          Wire.endTransmission();
       last_update = millis();
    }
}