It may sound surprising, but your watch display screen is quite often the culprit behind battery drainage. Thankfully, there are a couple of things you can try: First, decrease your watch’s screen brightness by going to your display settings (either directly on your watch or via the Wear companion app), and, depending on your device, either tapping and swiping the Brightness meter to the left, or tapping the minus button. You can also alter your watch’s display automatically by toggling on “Adaptive brightness.”
Adjust how long it takes for your screen to timeout by tapping “Screen timeout” in your display settings – selecting the fastest option, 15 seconds, will help you save battery life. Finally, don’t forget to check that the “Always on Display” setting (called “Always on Screen” on some devices) is toggled off.