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FWIW, saw the same thing with a new 38mm SS...turning off location services for passbook on the paired phone seems to have solved the problem.
 
I recently moved to a SS SB Apple watch from a Sport and notice horrible battery life for until last night when I wen through the Apple Watch app and notice that some of the apps were still "installing" even though they had already been installed. So I uninstalled and reinstalled.

It seems to be a bug in unpairing and pairing process. that some apps stay in the "installing" phase indefinitely draining the battery. I could be even worse if you are testing apps with Apple Watch functionality via TestFlight as take longer to install and have to be managed in the TestFlight app.
 
I still believe it takes several days to a week to get an accurate picture of battery life. There's a lot of syncing going on when you first get it and if you un-pair the watch you're essentially wiping it and starting over at day one. One thing I did that has made a quite noticeable difference in battery life was to enable "Reduce Transparency" in the Apple Watch app accessibility settings. That also improved the readability of all the screen alerts I receive. I understand that enabling "Reduce Motion" will also increase battery life although I haven't done that. Mine is quite good now as it is.
 
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