Especially after I've used the exercise app. I've been to the store and the battery is fine. I have been rebooting and re-pairing the watch to fix the problem which it does only to return after a workout. Really annoying.
Its going to happen with usage and being that it is a first gen device. Maybe turn off things like background app refresh or other apps or settings that you don't need.
I use the exercise app every day and when I put on charge at night it rarely has over 50% usage. Running latest OS on both phone and watch. I have the watch on 12 hrs a day and use the watch often during the day (including HR monitor) and have the weather apps updating frequently. I have read others with battery drain but don't know what the missing link is between mine and those.