Well, on my side the same. From one day to another, battery life dropped from 3+ days to <10 days. It was with the upgrade to 4.0.0.7. Hence, for sure, I expected this to be a bug, which came with the upgrade. Optimizing everything possible (without losing main functionality of a smart watch), I was able to reach 12-14h without special activity.
I tried any "hotfixes", I found in google. resetting watch, reinstalling phone apps, clearing caches, avoiding restore from backup, even avoiding logging in to Samsung. After 6 weeks, I decided to bring in a new orig battery. This helped to get to 18-20h. So, old battery lost a bit of its capacity, but not too much.
In the meantime, I flashed back to 4.0.0.2, which earlier ran for days with the old battery, without the situation getting better. Even going back to 2.3.2.4 (which was known as long-runner firmware), I just reach about 20h max. Be sure: even after flashing, I cleared caches, re-installed phone apps etc. to be sure, I am starting with the flashed firmware from scratch.
Partially, I am thinking about a hardware issue, that occasionally started at the same time when the upgrade came. But my watch never fell down or anything like that. Possibly a bug in the upgrade caused a part of the hardware to die?
Meanwhile, seeing so much people in the internet having the same issue with the frontier, I am kind of thinking about a predetermined breaking point or an internal "expiration date", that shall allow Samsung selling newer models.
But to be honest: with all the above and knowing what happened to so much Samsung watch users, I do not guess, the next watch will be a Samsung.