Sony PHA-3 sounds great

the Sony PHA-3 sounds fantastic-with 10-strikingly precise and musical as the portable Onkyo quality headphones such as Ultimate Ears UE.
He has indeed a built-in battery;
see more about Sony PHA-3:
"Power DC 3.7 V: Built-in lithium-ion rechargeable battery," DC 5 V: when charging via USB;
Type of Use: Portable and Home
Recharging time: Approx. 15 hours (PC Connection) USB Micro-B input (for charging & PC) Power
Battery Type: Built-in lithium ion rechargeable battery
Power Source: DC 3.7 V Built-in lithium-ion rechargeable battery
Battery Life (Approx): Digital (balanced) connection: Approx. 5 hours; Analog connection: Approx. 17 hours
Battery Indicator: Yes: Lights up green when Power is turned on, flashes to indicate battery level. See manual for details.
Battery Charging (Approx): Charging via USB: Appox. 15 hours from empty to full
Red Battery Charge LED on during charging
LED indicator turns off automatically once fully charged
Unit will not charge During Playback
Output Power: Maximum Output: Approx. 320MW 320MW + (Balanced Connection, 32 Ohms, 1% distortion)
Input Voltage: Maximum: 2 Vrms (AUDIO IN)