Sony BF-TDSY Wireless Headset Compatible Battery 1.2V 700mAh

Sony MDR-DS3000 / MDR-DS4000 Series — 1.2V Ni-MH Replacement Battery (1-756-316-21)

This is a 1.2V 700mAh Ni-MH cell that replaces the original rechargeable pack in Sony wireless headsets. It fits the BF-TDSY, MDR-DS3000, MDR-DS4000, MDR-IF140, and over 20 additional compatible models. When the original cell degrades and the headset stops holding charge, this cell restores full function without replacing the entire headset.

• Multi-model fit across the Sony wireless headset range: These headsets share the same 1.2V Ni-MH cell format, connector pinout, and base-station charging circuit. The BMS handshake is consistent across the MDR-DS and MDR-IF lines, so the same cell works across all listed models without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a Sony MDR-DS3000 base station. The BMS accepted the new pack without error, completed a full charge cycle, and the headset registered correct charge status on the base unit display.
• First-cycle base station registration: Place the headset in its base station and allow a complete charge cycle before making any calls. DECT headsets log the new cell during that first full cycle — skipping it causes the base to display inaccurate talk-time estimates from the start.

Base station not recognising a new pack after cell replacement

Sony DECT base stations run a handshake with the headset's cell during the first charge. If you seat the headset and the base shows a charging error or no charge indicator, the BMS has not completed initialisation. Remove the headset, reseat it firmly, and leave it undisturbed for a full charge cycle. The base station needs sustained contact to log the new cell — interrupting the first cycle resets the process.

Headset cutting out mid-call on a freshly charged battery

This happens when a new Ni-MH cell has not yet reached full capacity through conditioning. On the first few cycles, the cell delivers less than its rated 700mAh because the nickel-metal hydride chemistry needs repeated charge and discharge passes to activate all available capacity. The DECT radio and audio circuit together draw enough current to expose this shortfall as a voltage sag, which triggers the headset's low-battery cutoff. Run three to five full charge and discharge cycles and the cutoff point will shift back toward the rated capacity.