Battery indicator on I watch ?..

You can also add a battery complication to your chosen Apple Watch face, which will show the battery level all the time.

See how here --> Change the watch face on your Apple Watch - Apple Support

Note: You may find adding complications to your chosen watch face simpler using the Watch App on your iPhone. Open the Watch App, then tap your watch face at the top (or choose another watch face from the Face Gallery) and add available complications there. Choose set as current watch face when done.

you swipe upwards from the bottom of the watch screen

Check your battery and charge your Apple Watch - Apple Support