Car battery drained after letting car sit for a day or two. Is it due to the cold weather?

My car hasn't had any issues when it comes to the battery/alternator in awhile. About 2
weeks ago when i tried starting the car it wouldn't start and was making a clicking sound.
Turns out the battery was drained. I assumed it was either because over the weekend I
didn't drive it and the weather dropped or when I start the car with the automatic start,
after 15 minutes the engine would turn of but the lights would stay on. I took the car to
get the battery checked and they said it was fine and that when the lights stay on after
the automatic start goes off was causing the battery to drain. So I then decided to take off
my headlights off of automatic so it doesn't drain my battery when I do the automatic
start. But then the battery was dead again recently. I did't drive the car for 2 days but one
of the 2 days I turned on the car to make sure the battery didn't die and let the engine
warm up. I didn't do that the next day because I assumed it was fine. Then the day after
that the car wouldn't start. Is this because of the cold weather or is something else
draining the battery? I made sure radio, lights, etc are all turned off before I leave the car.
I really do not know what is causing the battery to die.