The altimeter loses calibration at night

Just wondering if it really represents a problem for you since per the 265 manual 

Auto Cal. -Allows the altimeter to self-calibrate each time you use satellite systems.

If it fixes it's self each time an outdoor activity is done, seems like a no harm, just a curiosity?.

It is true that it is calibrated with each activity. But it is interesting that it works correctly for storm prediction, since this error in the altimeter affects the barometer.

Storm alert just observes changes in air pressure over short time, so altitude calibration (correct or incorrect) doesn't affect it.

What you say is totally true. But one situation that can occur is that if this calibration occurs in the middle of a sudden drop in pressure, it probably won't warn you about it. I see that calibration at midnight as useless, it doesn't help, it's the opposite. There are times when I don't do any activity but if I'm walking and in the mountains, that's when I won't be able to trust the altimeter unless I calibrate it myself every morning. I know that it has to be calibrated from time to time, but every night and on top of that doing it incorrectly. I also appreciate your answer 

Do you happen to sleep upper floors? Because the nightly altitude uses your phone to get location (since watch's GPS doesn't work indoors) and do its calibration based on the assumption that your are on ground level.

If I remember correctly you can do manual altitude calibration to correct altitude in the place where you sleep, and then the altitude for that place is remembered and the nightly altitude calibration should use that altitude. I've personally never tried it though, since I sleep on the ground floor.

Thanks, I'll try to calibrate it before going to sleep. To calibrate it, do I just perform a manual calibration before going to bed and that's it?

I think so (but I haven't tried it myself, as I wrote). The following page is for Fenix 7, but since 265 also has barometric altimeter, it should probably work the same way.

support.garmin.com/.../

Thanks!