Plantronics 64327-01 Replacement Battery 3.7V 240mAh

Plantronics CS50USB / 64399-01 Series — 3.7V Li-Polymer Replacement Battery (64327-01)

This is a 3.7V, 240mAh lithium-polymer replacement battery for Plantronics DECT and wireless headsets including the CS50USB, 64399-01, and 65358-01 series. It slots into the headset housing and powers both audio processing and the DECT radio simultaneously. OEM part numbers 64327-01, 64399-01, and 65358-01 all cross to this cell.

• CS50USB and CS5x platform compatibility: These headsets share a common cell format, connector pin-out, and BMS handshake protocol with the base station. One cell covers the full cluster because the voltage rail and charge termination logic are identical across the range.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a CS50USB base station. The BMS completed its handshake, charge termination triggered correctly at 4.2V, and the base station cleared its charging error indicator without intervention.
• First-cycle base station logging: On first use, seat the headset in the base and let it complete one full charge cycle before taking any calls. DECT base stations log the new cell's state-of-charge curve during that first cycle — skipping it produces inaccurate talk-time estimates on the base display.

Why the CS50USB base station shows a charging error after a cell swap

The CS50USB base station communicates with the headset's BMS before it starts the charge cycle. If the new cell arrives at storage voltage — typically around 3.6V — the base may flag a fault because the voltage sits outside its expected handshake window. Seating the headset firmly and leaving it undisturbed for 10 minutes usually allows the BMS to initialise and the base to clear the error. If the error persists, remove the headset, wait 30 seconds, and re-seat — this resets the handshake sequence from the beginning.

Headset cuts out mid-call despite showing a full charge on the base

This happens when the cell is still at storage voltage and the base display hasn't updated after a proper charge cycle. Under combined DECT radio and audio processing draw, the cell voltage sags below the headset's cutoff threshold faster than the display suggests. The fix is straightforward: complete one full uninterrupted charge cycle in the base station before use. After that first cycle the BMS recalibrates its state-of-charge reading and mid-call cutouts stop.