I've found that the latest watchOS has made my battery (S2-Nike) usage much worse. Some days, the battery lasts the normal amount, which is typically 65-70% remaining by quitting time. After the update, the range has been around 40-60% by quitting time.
One day in particular, I had horrendous battery usage. By night time, I was down to 25%, which never happens. So I checked the watch battery usage times. On that particular day, I was at around 11 hours use time and 16 hours stand-by. Use time is never that high of a percentage, so I've been tracking the ratio that last couple of days.
Looks like normal usage for me is about 20% use time against stand-by. So for an 18 hour day, I should expect around 3 to 4 hours of use time.
Take a look at your battery stats to see if you have unusually high use times.