WatchOS 4 on Original Apple Watch

Since upgrading to WatchOS 4 on my original Apple Watch the battery usage is inconsistent. some days I get just slightly less than I used to get on WatchOS 3.x other days I get about half the usage (if not less).

I can't say for sure but the times where it drains faster I've used my AirPods to listen to music on Apple Music. But the strange thing is I'm listening from my iPhone 7 Plus, as I put no music on my watch.

Anybody else noticed this?