About this replacement
Sony SRS-XB501 Series — 7.4V Li-ion Replacement Battery (ID659B)
This is a 7.4V, 6700mAh Li-ion replacement battery for the Sony SRS-XB501 and SRS-XB501G portable Bluetooth speakers. It replaces OEM part ID659B. When the original cell degrades and the speaker stops holding a wireless charge, this restores untethered playback.
- SRS-XB501 and SRS-XB501G compatibility: Both models run on the same 7.4V battery rail, share the same connector pinout, and use the same BMS handshake protocol — a single cell covers both variants without any modification.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the SRS-XB501 chassis. The BMS accepted the pack cleanly, balanced the cells without error flags, and the fuel gauge calibrated correctly within the first full cycle.
- Monthly discharge cycle for the SRS-XB501: Speakers left on a desk and topped off daily never hit a meaningful discharge depth. Let the SRS-XB501 drain below 20% at least once a month before recharging — constant shallow cycling causes fuel gauge drift and accelerates cell capacity fade over time.
Why the SRS-XB501 runs warm inside its fabric housing during long sessions
The SRS-XB501 wraps the amplifier board and battery pack tightly inside a fabric and rubber housing with limited airflow. At high volume, the Class D amplifier generates heat, and the Li-ion cell adds its own discharge heat alongside it. Both heat sources share the same enclosed cavity. If the housing feels uncomfortably warm after extended play, drop the volume by 20–30% — this reduces amplifier draw and lowers combined thermal load on the pack.
Audio distorting before the battery indicator reaches empty
This happens when cell voltage sags under combined amplifier and Bluetooth radio draw before the fuel gauge registers low battery. The amplifier clips because the supply voltage has dropped below what it needs to swing full output — even though the indicator still shows charge remaining. It is a voltage sag symptom, not a speaker fault. Recharge the pack when distortion starts; the cell is running below 6.8V under load at that point.