Is my Apple Watch Ultra traceable when powered off or when the battery goes flat?

Unless the watch connects to a Wi-Fi or cellular network, the watch can not be located, or if more than 24 hours have passed, since its last location was sent to Apple.

If your Apple Watch is lost or stolen - Apple Support

Find your lost Apple device or AirTag with Find My - Apple Support

The Apple Watch Ultra can be located via Find My, but when it’s powered off or the battery is dead, the app will usually only show the last location it had while still on.