Whatever it was in iOS 13 that was MURDERING the battery on my Series 1 watch was resolved either by upgrading to 13.1, or by removing the new Reminders App from my phone. 🤷🏻‍♂️

Update: I think it’s Reminders. I reinstalled and in 1 hour the watch battery dropped 12%.

In the previous 14 hours, it dropped 54%, less than 4% per hour. 🤔