Apple watch series 4 battery is draining faster than ever

Hi all, need your help here. I have been using my apple watch series 4 since June 2019 and everything went fine until today. Early today I discharged my watch at 100% and I saw that the battery went to 77% in only 2-3 hours for nothing (did not use the watch totally) then I charged it again to 100% and I think it took longer than usual.

Later today I used the watch to navigate music play and realised that the battery is draining. Listened to only 3 songs through airpod (airpod is connected to iPhone) while walking and battery was consumed by 10%. I don't think this is normal as I used to listen through airpod for at least 5 hours a day and the battery remained around 30-40% at the end of the day. And by the time I type this, the battery is out for 3%, this is totally not normal I suppose?

For information, the software installed is 6.0.1 and always connected to iPhone's bluetooth (iOS 13.1.3). The only thing change from previous battery's habit was I reset the watch to connect with new phone. I did this mid this week yet the draining only happened today. Is this something related to error in reseting? Or battery issue? Anything I can do to solve this?

Thank you!