Why is my Apple Watch Series 8 battery draining so fast?

There's multiple things you can do to adress this:

1. Double click the Digital Crown fast, then swipe all open apps to the left to close them. This will make sure no unnecessary background apps drains the battery.
2. Make sure you're running the latest watchOS by going into Go to Settings > General > Software Update. An older and less efficient watchOS version might drain your battery.
3. Go into Settings > Battery > Enable Low Power Mode. This will significantly extend your battery life.
4. Go into Settings > Battery > Battery Health > Enable Optimized Battery Charging. This will make sure your Apple Watch charges in a way that extends the life of the battery in your Apple Watch.
5. Go into Settings > Battery > Battery Health and see if your battery has a low battery health percentage (percentage under 80% is considered bad). You can take your Apple Watch to an Apple Store to get the battery replaced.

The Battery Health on your Apple Watch has downgraded because if you charge your Apple Watch to 100% that can effect the Battery Health on your Apple Watch make sure to save your Battery Health charge your Apple Watch to around 80 or 90 Percent To make sure you Apple Watch doesn’t die a lot go to a nearby Apple Authorized Store or a store that can replace your battery and give you a new battery so you battery health is at 100% and your Apple Watch battery will not die fast

BTW, there was no reason to post this 3 times in the watch forum!

M1 Mac mini, macOS 15.3.1;  Watch, series 10 GPS-only, watchOS 11.3.1; iPhone 16, iOS 18.3.1; TV 4th Gen, tvOS 18.3; HomePods, audioOS 18.3 and Airport Express w/ Airplay 2