At least the noise level detection application running in the background does not impact power reserve that much for me. I am just running a test on that. Same scenario as yesterday (described above), but cellular data not activated. Noise level detection running in the background. I am not sure, how many trainings I will log today. Probably one less than yesterday. I will report back tonight. At the moment I am three hours and ten minutes into the usage day (started again at 05.30 am and now it is 08.39 am as I am writing this) and the battery is draining at a rate of approx. 4% per hour, which looks pretty normal.
Just to follow up on my posting from above.
I kept testing my Apple Watch (Series 5, 44mm, natural Titanium) over the last few days, also with watchOS 6.1. Use case is as described in my very first post in this thread. In short: everything is switched on that can be switched on: all antennas, als Siri functions, noise level detection, always-on display etc.
I am a very active Apple Watch user, I log 2-3 trainings a day, use it for messages, emails, short phone calls. Most of the time the watch is attached to its paired iPhone, less often on WiFi and from time to time it runs on cellular.
I get at least the full promised 18 hours out of it EVERY day, it never gave up on me before that, on many days it runs even longer.
As far as I can determine, the worst power draw comes from extended time on cellular networks.
For my regular use case that power consumption is approximately 5.2% per hour. If I switch off noise level detection and cellular connectivity and log less trainings, I can get it down to just above 4% per hour.
So all in all, I am still pretty pleased with battery life on my watch.