Hey so I need help picking an MP3 player. I need one with at least 6 hours of continuous battery life, however even more would be better. It also needs a lot of memory. So one with 16+ gbs of space, or one with an sd card slot. I'm not sure if any like this exist but I would also like it to have an interface similar to Spotify. I'd like to spend less than 50 dollars but if you know one that fits my description for more than that please share. Thanks :)

I honestly don't see why would you want an mp3 player whatsoever. They are overpriced and outdated by today's standards since most of them are not being manufactured anymore.
If I was you I'd simply buy some cheap second hand phone with fucked up screen or whatever with that 50$ and use that instead.
However if you really want an mp3 player for some reason I'd suggest this. I have personally used it few years ago and it served me well with 16 GB storage and ~5 hours of play time when fully charged :)
Oh and also if I remember it right it has an sd card slot as well

Can phones play MP3 files

Sorry in not good with tech :/. Any way thanks