Apple Watch battery drains in a day

From: Apple Watch Battery and Performance - Apple Support

section on: Battery and performance management [with reference to the Watch]

"If your device performance has been impacted by an aged battery and you would like to get help with a replacement Apple Watch, contact Apple Support." Click here for Apple Support --> Contact - Official Apple Support

You didn't mention what model Apple Watch you have.

I have had to charge my Series 5 watch daily since the day I bought it. And lately, I've had to turn off the Always On feature to even get it to last the day.

Mentioning this because there may be nothing wrong with your watch battery. (And, of course, this depends on the apps you have on your watch...in my case, I have a couple of "hungry" ones).