We've all had battery issues with our watches lately, especially the ones that have iOS 13 beta updated on their iPhones. I've been pretty annoyed by it as the Apple Watch battery runs out of battery before I go to bed.
I usually charge my watch when I'm home after dinner and charge it off before I go to bed. It usually charges up to 100% fairly quickly, so I don't feel the need to leave it on charge overnight. However, that was exactly what I did two nights ago, and yesterday the Watch battery was back to normal. Before bed, my watch was still charged up to 50%. I left it on the charger overnight last night, and today as I write this, my battery problem is resolved.