Yay! This is my favourite problem.
There are a couple of factors that could be at play here.
1. When the temperature is low, the battery cannot provide as much power as when temperatures are more normal.
(In my case, I've seen the displayed range to be lower in the morning when I arrived at work, than in the afternoon when I'm leaving work)
This is because the battery has warmed up as the day warms up.
2. There could be a timer set up to pre-heat the car.
When I first bought my car, I was having significant power drain going on overnight.
One evening, I went out to retrieve something from the car and found the interior to be blazing hot.
Once I found the timer settings, I discovered that the car had been set up to pre-heat the interior first thing in the morning, and at 7pm in the evening. Naturally that was using a lot of power from the battery.
Checking for pre-heating (or cooling) timers is probably the most important thing for you to do now.
If you poke around in the forum, you'll find me banging on about this timer issue, this was my original post on the subject:
https://www.myoutlanderphev.com/forum/v ... hp?p=19759