Does Garmin changed something Today, to improve battery life?
After 8h as smart watch (no activities) I still have 99,4%.

After a couple of charge cycles my 945 has settled down to about 0.3%/hour of battery drain. That is with Bluetooth, OHR, PulseOX during sleep, and messages on. I am pretty sure I can get to the advertised 14 day battery life if I turned off PulseOX which seems to drain a lot of battery overnight. On a side note, the advertised 10 hours with GPS and music on has proven to be a very accurate claim by Garmin.