Thanks for your answer.

I need to continue to use the M5Stack Core as I have made some backplane electronics and need to use the M5Stack stock.

I didn't know about this post and I already used a diode and had a bug with the ESP. Probably this problem of low battery charge.

The idea is great to use a MAX40200 but it requires extra wiring.

I tried with a capacitor. I have some 4700µf in stock at 63V.

I like this solution, no modification and it works well.

I will test it over several days.

For a quick fix, purchase and use the Core2 instead.

For a DIY fix, read through the details of this thread:
https://community.m5stack.com/topic/1822/no-reset-when-usb-power-removed-solved

#include <M5Stack.h>

// the setup routine runs once when M5Stack starts up
void setup() {

// initialize the M5Stack object
M5.begin();

M5.Power.begin();

// Lcd display
M5.Lcd.fillScreen(WHITE);
delay(500);
M5.Lcd.fillScreen(RED);
delay(500);
M5.Lcd.fillScreen(GREEN);
delay(500);
M5.Lcd.fillScreen(BLUE);
delay(500);
M5.Lcd.fillScreen(BLACK);
delay(500);

// text print
M5.Lcd.fillScreen(BLACK);
M5.Lcd.setCursor(10, 10);
M5.Lcd.setTextColor(WHITE);
M5.Lcd.setTextSize(1);
M5.Lcd.printf("Display Test!");

// draw graphic
delay(1000);
M5.Lcd.drawRect(100, 100, 50, 50, BLUE);
delay(1000);
M5.Lcd.fillRect(100, 100, 50, 50, BLUE);
delay(1000);
M5.Lcd.drawCircle(100, 100, 50, RED);
delay(1000);
M5.Lcd.fillCircle(100, 100, 50, RED);
delay(1000);
M5.Lcd.drawTriangle(30, 30, 180, 100, 80, 150, YELLOW);
delay(1000);
M5.Lcd.fillTriangle(30, 30, 180, 100, 80, 150, YELLOW);

}

// the loop routine runs over and over again forever
void loop(){

//rand draw
M5.Lcd.fillTriangle(random(M5.Lcd.width()-1), random(M5.Lcd.height()-1), random(M5.Lcd.width()-1), random(M5.Lcd.height()-1), random(M5.Lcd.width()-1), random(M5.Lcd.height()-1), random(0xfffe));

M5.update();
}

https://photos.app.goo.gl/SK2xeaiBvxcBfyHE8