Apple Watch battery draining fast

To understand Apple Watch performance and its relation to your battery, see:

Apple Watch - Battery - Apple

Apple Watch Battery and Performance - Apple Support

“Battery life” is the amount of time your device runs before it needs to be recharged. “Battery lifespan” is the amount of time your battery lasts until it needs to be replaced. Maximize both and you’ll get the most out of your Apple devices, no matter which ones you own. See the "Tips for Apple Watch" section in:

Batteries - Maximizing Performance - Apple

If the battery drains too fast after an update, see all the replies to:

has anyone had battery issues with the 10… - Apple Community

Battery Drain since watchos 7.4 - Apple Community

WatchOS 7.5 battery drain - Apple Community

FWIW, in some cases, unpairing the watch, completely erasing it, then pairing and restoring the backup will resolve the battery draining issue after an update. (Simply unpairing and pairing again may not work.)

Unpair and erase your Apple Watch - Apple Support

Also, some people have found that simply waiting a few days after an update resolves the battery draining problem.

Also see:

Apple Watch battery drain - the ultimate … - Apple Community

Some users report that a hard reset resolves this issue.

Other users report that powering the watch off and turning it back on has resolved the issue.

Power off an Watch by pressing and holding the Side Button. When the sliders appear, tap the power icon in the upper right corner.

To turn the watch on, press & release the Side Button.

M1 Mac mini, macOS 14.4.1;  Watch, series 7 GPS/cellular, watchOS 10.4; iPhone 12 Pro, iOS 17.4.1; TV 4th Gen, tvOS 17.4; HomePods, audioOS 17.4 and Airport Express w/ Airplay 2