About battery draining, I did some specific tests and I can confirm that the issue is present and that it related to the zombies file transfers.

Are you sure about the simulator? My understanding is that the Simulator app doesn’t support the transferFile(_:metadata:) method at all.

I did not notice the battery draining issue. Did you try to apply the custom message workaround and to clean up zombies file transfers checking the progress?

@AngryS about the workaround I am following the same approach suggested by @cfc and @JackAardal adding a specific custom message https://stackoverflow.com/questions/78569322/missing-wcsessiondelegate-didfinish-callback-transferring-file-from-watchos-to-i