Only charged it up to 87% before I left for the day. Battery health is at 77%, took this screen shot at 12:52 AM EST so just a little bit over 12 hours.
Full work day so lots of notifications, texting and two short 2 min phone calls. My Series 4 is still a workhorse even at 77% capacity. In theory if I charged it to 100% before leaving I should have around 27%.
Those with WatchOS 10 battery issues should consider unpairing and re-pairing because it's likely a rogue app/bug causing it.
Walmart has a 1st gen SE right now for $109. Exactly the same as an S4 except it’s missing the ECG feature.