First night having my new Series 4, went to bed with it at 100%, woke up with 92% about 6.5 hours later. Right now it's at 52 percent with minimal usage.
Either the hard reset or uninstalling Overcast on the watch seemed to solve the problem for me. I have reinstalled Overcast but turned auto-sync off since I always have my phone with me anyway.
Had this exact issue after updating to 5.0.1
Ironic indeed. Put it on the charger a day after upgrading. Picked it up off the charger in the morning (full night on charger) and it was at 55% !!
Updated watch to 5.0.1 before bed, put watch to charge (at 55%) and confirmed that it was charging. Woke up and battery was drained. Coincidence or something to do with 5.0.1?
[doublepost=1539201064][/doublepost]This update was supposed to fix a charging problem. My watch was fine before Watch OS 5.0.1 , since this update it never charges fully no matter what percent it is at when it goes on the charger. My watch charges through the night while sleeping 10-5. I unpaired my watch and went through all the steps to fix it, Apple support even did a diagnostic on the hardware, which is fine. I even tried another charging cable, still the same problem. Sounds like it could be a software bug.