Under current technology, a player’s sound quality is proportional to its power consumption. Many famous DAC chip on the market go with 5V power supply since desktop device has very large operating current. Meanwhile, the high quality headphone amplifier also requires high voltage and current supply.
Therefore, the sound quality is a contradiction to its playback time on the basis of limited dimension. For former FiiO music players, we set 10hrs as a standard since I personally think 8hrs of playing time is the basic requirement to any portable devices. Considering that not so many people would listen to the music as long as 8hrs per day, it seems that a little shorter playback time can be accepted as well.
Anyways, I leave it to you to discuss.