Battery drop when parked outside

I recently bought an ID3 Pro S. As of today it's two months and less than 3000 km old. My experience so far has been great! It feels very agile, spacious inside and quite comfortable to ride. Autonomy is good, too. We did a 400 km trip this weekend and we only stopped for 15 min to stretch a bit and have some fresh air. We charged about 20% at 75 kW meanwhile, but we could have make the 400 km without problems if we wanted to!

We charged the car to 80% when we arrived and parked outside. Three hours later the battery dropped 2 %. During the night it dropped another 1%. Any idea why this could be?