Why does the YouTube app drain my iPhone battery quickly?

When I first got the app, the battery just depleted normally for itself and it was fine. But now it's just getting worse. I even have low-power mode on, Wi-Fi, etc. And still whenever I'm watching YouTube videos, the battery just drains really quick. Has anyone else had this problem? Could it be something else, or does the sound normally take a lot of battery? Is there anything I can do with my phone so that the battery lasts longer? By the way, I have an iPhone 6s.

IPhone 8 or iPhone X?

I don't want the plus because I don't really want a big phone. The pros of getting the 8 is that it's $300 cheaper than the X for the same processor and basic functions. The only reason I'm considering getting the iPhone X is because it has an extra 2 hour battery life and that s cool for someone like me who's out of the house a lot, it also has the face recognition but honestly, I could care less about that, I never had a big problem with the Touch ID and they re also adding a tier 2 Touch ID.

Will the iphone x still have shortages?

I read a few days ago that the iphone x is in low production right now so there may be shortages, but with apple delaying the release until november, do you think there will still be shortages?