I'm playing a mix of FLAC and MP3s, airplane mode, and sometimes switching between Neutron and Native player.
After 7.5h, I have 25% charge left from full, which conveniently translates to 10% per hour, or about 10h playtime.
The official specs list 25h of playback for 128kbps MP3. Should I be expecting much more than 10h, especially considering display and wifi is almost always off?
What playback lifetime are you getting?