Sony SRS-X3 Replacement Battery ST-01 7.4V 2600mAh

Sony SRS-X3 / SRS-XB2 / SRS-XB20 — 7.4V Li-ion Replacement Battery (ST-01)

This is a 7.4V, 2600mAh Li-ion replacement battery for the Sony SRS-X3, SRS-XB2, and SRS-XB20 portable Bluetooth speakers. It matches the OEM ST-01 pack in voltage, capacity, and connector pinout. Fit this battery when the original no longer charges fully or drops power unexpectedly during playback.

• SRS-X3, SRS-XB2, SRS-XB20 compatibility: All three models share the same 7.4V dual-cell Li-ion architecture, the same physical footprint, and the same BMS handshake protocol — which is why Sony used one part number, ST-01, across all three. Swapping between them requires no modification.
• Bench tested on actual hardware: We ran this pack on an SRS-XB2 unit and monitored BMS charge acceptance from flat. The protection circuit engaged at 8.4V full-charge cutoff and held low-voltage cutoff at 5.6V — both within Sony's factory spec for this cell configuration.
• Fuel gauge reset after fitting: On these speakers, the onboard fuel gauge can misread state-of-charge if a new cell is installed without a full charge-discharge cycle. After fitting, charge to 100%, run the speaker until it auto-shuts off, then charge again — this calibrates the indicator so the battery level LED reflects actual remaining capacity.

Capacity fade from constant desk-top charging on the SRS-X3 and XB20

These speakers are often left on a USB charge cable between uses, which means the cell spends most of its life sitting at or near 8.4V — the top of its charge window. Li-ion cells degrade faster at sustained high state-of-charge because elevated voltage accelerates electrolyte oxidation at the cathode. On the SRS-X3's compact housing, there is also limited thermal dissipation during charging, which compounds this stress. Discharge the pack below 20% at least once a month before recharging to slow this degradation.

Audio distorts before the battery indicator reaches empty

This happens when the cell voltage sags under the combined current draw of the amplifier and the Bluetooth radio — particularly at high volume. The amplifier clips its output signal before the BMS trips the low-voltage cutoff, so the speaker sounds distorted while the LED still shows charge remaining. The root cause is internal resistance rising in an aged cell — even a new-looking battery with shallow-cycle history can show this. Replace the pack and confirm resting voltage reads above 7.0V after a full charge before fitting.