9 hours? That is impossible !
It lasted 9 hours when playing music for 9 hours continuously ?
Just sharing my usage time man, I have no reason to fabricate or lie over a DAP I don’t even own anymore. Roughly 9 hours with normal use, screen on periodically to change tracks etc, Spotify offline music. The AMP 9 was the best battery life I was ever getting out of the DX220. Regardless I think 4 hours for AMP 9 is crazy low, sounds like there may be something going on with your unit.