The battery life of the Garmin Fenix 7 is impressive, especially under mild usage conditions as you describe. On average, the battery life is about 14 days with 2 hours of GPS use per day, obviously a little less if you also use the heart rate monitor.
As for the cold, depending on how cold it is, skiing can significantly reduce battery life. As a rough estimate, you can expect to lose another 20-30% of typical battery capacity in very cold conditions.
MfG Anton

Battery life is 15 days if the watch is worn without activity.
Activity with GPS for a few hours a day will reduce the battery life by a few days and without activity by a few hours. But the watch will last a week. Enormous progress has been made between the Fenix 5 and subsequent models. Garmin give specifications on their site according to use cases.

Yes, it also lasts about 8 days when skiing

About 13 days