About this replacement
Sony SRS-X11 — 7.4V Li-Polymer Replacement Battery (ST-02)
This is a 7.4V, 1000mAh Li-Polymer replacement for the ST-02 battery inside the Sony SRS-X11 portable Bluetooth speaker. It fits the compact SRS-X11 unit and restores wireless playback when the original cell has degraded. Voltage and capacity match the original pack exactly — 7.4V at 7.4Wh.
- SRS-X11 fitment: The SRS-X11 runs its Bluetooth radio and Class D amplifier from a single 7.4V Li-Polymer cell. The ST-02 form factor — 51.65 × 34.20 × 11.20mm — is specific to this housing. No other Sony SRS cell fits the cavity or meets the voltage rail the amplifier board expects.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the SRS-X11 board. The BMS accepted charge from the speaker's internal charging circuit without error flags, and discharge cutoff triggered cleanly before cell voltage sagged below the amplifier's minimum operating threshold.
- Monthly discharge cycle for the SRS-X11: If you keep this speaker on a desk and top it off before it drops below 50%, do a full discharge to under 20% at least once a month before recharging. The SRS-X11's fuel gauge drifts under constant shallow cycling, causing the indicator to read full while actual capacity has already dropped.
Why the SRS-X11 amplifier clips before the battery indicator hits empty
The SRS-X11 Class D amplifier starts clipping audio at high volume when cell voltage sags — even if the battery indicator still shows one or two bars. A degraded Li-Polymer cell has higher internal resistance, so under the combined load of the amplifier and Bluetooth radio, terminal voltage drops faster than the fuel gauge tracks. The indicator reads state-of-charge from a coulomb counter, not live voltage, so the two fall out of sync. Swapping to a fresh cell with lower internal resistance keeps terminal voltage above the amplifier's clipping threshold longer into the discharge cycle.
SRS-X11 not charging after sitting unused for several months
Li-Polymer cells left discharged for extended periods can drop below the minimum acceptance voltage the SRS-X11's charging circuit will recognise — typically under 3.0V per cell, or 6.0V for the 7.4V pack. When this happens, the speaker shows no charging indicator and the LED may blink an error pattern. If the original battery is in this state, it cannot be safely recovered and replacement is the correct path. Plug the new ST-02 in and verify the charging LED goes solid or begins its normal charge cycle within 30 seconds of connecting USB power.