Testing ESP32 w/battery


I’d like to know how long an ESP32 DEV board with a battery holder link would last using a battery BRC 18650 3800 mAh charged at 4.2V.

As a test, I´m using the following code which sends out an email every hour and then, it goes into deep sleep.

To my surprise, I only got 4 emails. Before reaching the fifth hour, the battery went below the 3.3V so the code stopped working.

It’s my understanding that the ESP wroom 32 draws approx. 150 micro amps when deep sleeping so, I expected the device to last days on that battery but, obviously I’m missing something here.

Am I running the test the right way?

#include <WiFi.h>

const char* ssid     = "****";
const char* password = "****";

// Time to sleep (in seconds):
const int sleepTimeS = 60 * 60; //1 hour
const int battPin = 36;  //SVP pin
const int ledPin = 16;

char server[] = "smtp.*****";
int port = 25;
WiFiClient client;

void setup() {

  pinMode(ledPin, OUTPUT);


  if (sendEmail()) Serial.println(F("Email sent!!"));
  else Serial.println(F("Email NOT sent!!"));


  Serial.println("ESP32 in sleep mode");
  ESP.deepSleep(sleepTimeS * 1000000);

void loop() {}


Done it but the current is so low that my DMM doesn't read it.