Battery doesn’t matter, check that crawling-interval is at -1 and enable-monitors is switched on.
Yes, both are on, also after logout/login,.
But localsearch is inactive (dead) after logout/login
Tried that?
Yes, a new user file is created after login again, and localsearch starts after a few minutes. Looks good, thanks.
All I have to do now is reconfigure my desktop dashboard and things. What else do I have to think about?
Nice to read that. If re-configuring your desktop is not a hassle, I think you are done.
Otherwise you may look for differences in the new and backed-up dconf files (leaving untouched the new tracker section of course).
An interesting development is that I cleaned up my test 15.6 install (which had a similar problem) since there was a mix of tracker related packages with version 2-0 and 3-0, removing all the 2-0 packages. After a
tracker3 reset --filesystem
and a reboot, text searching is enabled and tracker automatically starts on login.
Maybe that was the cause of your trouble too, the upgrade to TW didn’t cleanup all version 2-0 settings?
Anyway, if your problem is solved, this is the end of the story.
Have fun!
I confess, the user trick is much simpler than I expected. Sorry for my obstinacy 
What tool reveals the content of the user file?