The user needs to charge the Apple Watch every two days on average, but some users have noticed that the watch's battery may drain more quickly. Therefore, this update allows applications that are open on the Apple Watch to continue to draw power from the battery, and the Internet from the network to update new content constantly, but closing this update means that applications that are open in the background will run for a short period of time before they are suspended as well as suspended from use Internet and battery power.
Not all apps need to refresh in the background, but there are others that do, for example, the Workout app needs background app refresh; To ensure your workouts sync seamlessly with your iPhone. So if you need to extend battery life more than using this app's data, the solution would be to disable this update or select the apps you want to run in the background and disable the rest.
Extend Apple Watch Battery Life by Disabling Background App Refresh
On your iPhone, open the Watch app.
Go to General > Background App Refresh.
You can disable background app refresh for all apps using the toggle button at the top.
Or you can scroll down and just disable it for apps like Calculator and Camera Remote, and leave the apps you want.
Since Background App Refresh is enabled by default for all apps, this is worth checking every time you install a new app on your Apple Watch.