Had a call with Support today - they recommendet to me to wait another week…. What else could I do :D
And they did some check on my watch (I think, they just collected logs) and saw that my battery had 79% health and suggested to replace it, if my watch won‘t recover within the next week.
Let me think.. either my watch had 100% battery health (16 hrs. duration) before the update and it - coincidently - dropped to 79% (3 hrs. duration) after the watchOS update… then I would be curious to learn the math, where 20% of 16 hrs. are 13 hrs., while 80% are 3 hrs.
In the other scenario the watch battery had about 80% before the update and lastet 16 hrs. and has 79% after the update and lasts now 3 hrs.
All this points to the update / software draining the batteries and won‘t get better, if I would replace the battery for 120€ as suggested.
I assume the watch would last 3.5 hrs with a new battery, I will lack the money and still can throw it into the duster.
Btw. today the watch died during my workout, after 44:37 minutes. It sucks…