I may have more apps on my watch than most people have on their iphone.
AND my new watch does have the cell option so not have all these app work in the background will save power.
I did not do a clean install of my new phone and watch or turn off background and my normal 3 day battery watch life before became about 2 days for the first week.
I have just started adjusting items that will save power - like brightness - even out side I may still have it too bright.
My other watch is on beta but the Series 4 is normal released version.