Ignoring that Spotify uses approx 20% per hour of the battery during offline/streaming playback I have noticed that the Spotify App always seems to be running and according to my 'test' outlined below uses 5%+ of a full charge even if you never open the app. This seems wrong to me.
Full Charge without Spotify Installed
Spotify Installed, watched switched off battery recharged to 100% and then switched on.
After 1.5 days normal Usage - 56% battery used - 12% on Spotify despite the app not being opened. That is 6% of full charge going on an app that is never opened (nor added as f widget) etc.
Surely this is a bug???
Strange, I'm using Spotify all the time and this is how my battery stats are like. I'd rather say that there is something wrong with the battery not the software issue. My Watch lasts for 5 days easily with Spotify installed and used quite often.
On the other hand it would be nice if this all is redesigned by Spotify especially after a cooperation was announced when Note 9 was revealed. Not being able to change the volume when using the app as remote to control Spotify on the phone is quite frustrating. And the all doesn't show anything very often if phone is locked etc. and need to be unlocked and run Spotify to make it working on the watch.
Do you keep your WiFi on? This may cause the app connecting maybe
Just not sure how to answer the question about how I use Spotify so I'll try to make it clear. I do keep my music on the phone and I'm using the app to control Spotify installed on the phone as remote. I just open the app on the watch and I forget about the phone in my pocket. I didn't see any difference between music saved offline or streaming, doesn't affect the battery usage on the watch. Picture no 1 show what I exactly see when using the app.
I am using the bigger 46mm version and I know the battery is better but still I don't think you should see 1 day and few hours when your (if it's 42mm) is charged to 100%.
Picture no 2 show the stats of the Watch 42mm which belongs to my girl. Estimated time is nearly the same as yours but there's 69% battery left. And she does have Spotify installed she just didn't use it since yesterday so you can see it on the lot but the app does not cause any draining issues.
I don't use the stream option in the watch app, I find this quite useless for me. Propably using this in stream option is causing the drain, I only use it for remote as mentioned before 
It is strange
This is really strange, I think there must some kind of correlation with other app. I've been using Spotify quite a lot today as remote (as mentioned before I do not use Wi-fi option cause the app doesn't allow me to log in for some reason) and my stats look like on the sreenshot.
Ho do you use the app? Stream on WiFi or remote?
If it's stream on WiFi I would suggest to turn on WiFi when Spotify I not in use, maybe this is causing the drain of battery when it's connected all the time.
