Sony WI-C600N Replacement Battery 3.7V 130mAh Li-Polymer

Sony WI-C600N / WI-C400 / WI-C500 Series — 3.7V Li-Polymer Replacement Battery (1-001-274-31)

This is a 3.7V, 130mAh Li-Polymer cell that replaces OEM part 1-001-274-31 in Sony WI-C series wireless earbuds. It fits the WI-C600N, WI-C400, WI-C500, and WI-C200, among others. The cell restores audio playback and active noise cancellation to earbuds whose original battery has degraded from repeated charge cycles.

• WI-C series shared cell platform: Sony's WI-C lineup uses the same compact 37.20 × 10.40 × 4.40mm Li-Polymer cell across multiple models. The shared voltage rail and connector spec mean a single replacement cell covers the range — no wiring modification needed.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on WI-C series hardware. The BMS accepted the new pack cleanly, completed the charge cycle without error flags, and noise cancellation drew current as expected without triggering any protection cutoff.
• First-cycle logging on WI-C earbuds: After fitting a new cell, run one complete charge before using ANC. The earbud firmware tracks cell state from the first full cycle — skipping this means the noise cancellation circuit may throttle draw early until the battery management system has a calibrated baseline.

Why ANC draw shortens cycle life faster than audio-only use

Active noise cancellation runs its DSP and microphone circuit continuously alongside the audio path, pulling a sustained combined load from a 130mAh cell. That sustained draw generates more heat in a compact housing than audio alone. Heat accelerates electrolyte degradation in Li-Polymer cells at this capacity. If ANC is not needed, switching to standard mode preserves more charge cycles over the battery's life.

Earbuds cut out mid-playback despite showing charge remaining

This happens when the combined audio plus ANC draw creates a brief voltage sag that crosses the BMS low-voltage cutoff threshold — even if the displayed charge level looks healthy. At 130mAh, the cell has little headroom to absorb a sudden load spike. The BMS trips as a protection response, not because the cell is empty. Confirm cell voltage reads at least 3.7V with the earbuds powered off; if it reads below 3.5V after a full charge, the replacement cell needs one more full conditioning cycle before voltage stabilises.