Poor battery lite

Depending on which model of watch you have it could have a naturally dying battery,check the battery health figure in settings/battery/battery health.

Batteries - Maximizing Performance - Apple

At 80% battery health it is recommended that the battery be replaced,you're getting quite close to that;

Pick the most minimal watch face you can - the more black and the fewer animated graphical elements, the less power-hungry it will be. We stay well away from the pretty butterflies, cartoon character and kaleidoscope options, plumping instead for the X-Large clock face in purple - but the least detailed and colourful 'Simple' clock face would probably be the most battery-efficient option.

In the Apple Watch app go to General > Accessibility > Reduce Motion and turn on Reduce Motion. This will limit animation and automatic resizing of the Apple Watch user interface on the Home screen when you open and close apps.

Do you often raise your arm? Perhaps you drink a lot of tea, or when you talk you wave your arms around gesticulating. If that sounds like you, it might be wise to turn off Wake Screen on Wrist Raise, a feature that shows you the time and your alerts when it senses movement.

Another way to preserve a little bit of power is to stop your Apple Watch beeping when you receive notifications.

In order to receive and alert you of notifications on your Apple Watch, the device has to be in almost constant communication with your phone - a power-draining business. So be choosy about what you actually need to be notified of.

Of all the apps, there is one whose notifications you should pay particular attention to: Mail. If left to their own devices these will kill your battery, because the watch will be constantly pinging the iPhone to see if you have any emails.

If you suspect an app is using too much power, you can force-quit it. Force-quitting an app is not as obvious as it is on the iPhone, however.

To quit a watch app, open the app, hold down the side button until you see the power off message, then let go of the side button and now press and hold the Digital Crown dial until you return to the home screen.

Adjust screen brightness

The OLED display of Apple Watch provides great black levels with minimal power management, but it still needs power, and the brighter your screen is, the more it will require. One obvious way to remedy this is to lower the brightness of the screen

Turn off Hey Siri

Hey Siri is a great feature that feels like it was made for Apple Watch, but it is also one that is constantly listening to you when the screen is on, one mAh at a time. Some users have reported greatly improved battery simply by turning it off, which can be done from Settings > General > Siri on your Apple Watch. Doing so will seriously amputate the usefulness of your watch, but sometimes you gotta do what you gotta do.

Take it easy on calls

Still in the obvious category, it should be noted that according to Apple, talk time (aka phone calls) is the best way to deplete your Apple Watch battery. Try to keep you inner Dick Tracy in check, and unless it is absolutely necessary, try placing phone calls directly from your iPhone. This is its primary purpose after all.

Take it easy on music streaming

After phone calls, streaming music via Bluetooth to a wireless headset is the worst thing you can do to your battery, according to Apple. If you have your iPhone handy, simply stream the music over Bluetooth from the phone to the headset. Even doing so, you’ll still be able to control what music is playing from your watch, but it won’t take the battery hit that comes with it.

Reboot from time to time

If you’re experiencing what appears to be abnormal battery drain on your Apple Watch, remember that this device is basically a miniature computer, and like every computer out there, it actually helps to sometimes reboot it. Even if you don’t see any battery problem, it’s actually not a bad idea to reboot from time to time. To restart, simply press and hold the side button to power off, then press and hold again to boot it up.