I've heard that it's hard to judge an updated effect on battery life since early on the device is "indexing". Not sure if I know the specifics of what that term truly means but I'm curious how WatchOS4 affects the S1 battery life after a clean install / reset and after the first few days...
I have had the OS4 update for a few days now and I have seen a little bit of a swing of battery life.
Example - Monday of this week I put the watch on after a full night charge around 6:30AM. At 10:30AM I still had 100% charge. I had just over 70% at the end of my night which was around 10:30PM.
Tuesday started around the same of 6:30AM. At 10:30AM I was down to around 92% battery life and didn't notice any major difference in notifications, texts, or heart rate checks (which is what I mostly use it for outside of a workout 3 -4 nights a week). I ended the day under 60% life.
Yesterday reflected Monday almost to a tee with the exception of being around 68% at 10:30PM last night.
Again, no major change and unfortunately I haven't had the opportunity to do any workouts this week so really there is no rhyme or reason to the swing in battery life so far.
All that said, it's still really strong in my opinion.