Neutron Music Player for Android. Yes the UI is outdated, but the efficiency and feature set cannot be beat. It’s so efficient on battery life compared to both streaming music services like Spotify, or any other local music player Android app. And the feature set is incredible. The full parametric equalizer, built in frequency response correction for almost any headphone model you can name, volume normalisation, EQ presets, direct USB access to USB DACs to bypass Android volume or format limitations, crossfeed for headphones, and that’s just what I can think of now. I’m sure there are more features I haven’t even used yet.