It's a nubia Z9 max Elite (NX518J) equipped with Qualcomm's Burndragon 810 SoC running nubia's stock ROM.
I just installed and tried out Poweramp and it's amazing. However my phone got hot considerably quickly. After unplugging it from wired power, it drained 1% battery in less than even 1 minute. I then got rid of Poweramp without killing other backgrounds, my phone managed to survive for more than 7 minutes with 1%.
Later I installed Poweramp back and turned off equlizer, and the battery consumption fell to a reasonable speed. So it's surely equalizer's fault.
Ah, yes. I can remember that Musixmatch had the same issue if equalizer was turned on. So there's nothing to do with Poweramp.
Can anyone help explain this phenomenon? Quite a bunch of music players have this issue. It's confusing.