Battery drains overnight

I have a brand new Instinct Solar, which I've only used on a few minutes of activities. I charge it to 100%, and within a few hours just sitting at the home screen with a few notifications firing, the remaining battery has dropped from 24 days to 19 days (73%) and dropping... overnight it went down to 5%.

I have the latest firmware 18.54 installed. I've tried the soft reset (hold power button) and it didn't help.

I tried to call Garmin support in Australia but I waited on hold for a long time and never got to speak to someone.

Is it faulty? Should I return it to the place of purchase?