RTC Gives wrong time after few days

Other Hardware General Electronics
18

If your clock is off by several minutes per hour, this would suggest that the clock is either borked or that the battery in it is flat. If it was only a couple of seconds per day, you would have been able to fine tune it by setting the aging register:

#define DS3231_AGING_OFFSET 0x10

int8_t ds3231_get_aging_offset()
{
  //Returns the aging offset, defaults to 0
  Wire.beginTransmission(DS3231_ADDRESS);
  Wire.write(DS3231_AGING_OFFSET);
  Wire.endTransmission();
  Wire.requestFrom(DS3231_ADDRESS, 1);
  return Wire.read() & 0xFF;
}

void ds3231_set_aging_offset(int8_t offset, bool force_conversion = true)
{
  //offset = a value from -127 .. 127
  //force_conversation = force the clock to use the value immediately
  //Negative values will speed up the module.
  //A change of +/- 1 will adjust the time base by 0.12ppm
  Wire.beginTransmission(DS3231_ADDRESS);
  Wire.write(DS3231_AGING_OFFSET);
  Wire.write(offset);
  Wire.endTransmission();
  if (force_conversion)
  {
    Wire.beginTransmission(DS3231_ADDRESS);
    Wire.write(DS3231_CONTROL);
    Wire.endTransmission();
    Wire.requestFrom(DS3231_ADDRESS, 1);
    uint8_t ctrl = Wire.read() | (1 << 5);
    Wire.beginTransmission(DS3231_ADDRESS);
    Wire.write(DS3231_CONTROL);
    Wire.write(ctrl);
    Wire.endTransmission();
  }
}

The aging register should be set when the time is also set, usually after a battery replacement.

EDIT: By fine tuning the aging offset of one of my cheap DS3231 modules, it is only off by less than one second over a period of several (5 as far as I recall) months.

Setting time on a RTC from the ethernet