Sennheiser Flex 5000 Replacement Battery 3.7V 280mAh

Sennheiser Flex 5000 / Set 880 / RS 5000 — 3.7V Li-Polymer Replacement Battery (AHB571935PCT-03)

This 3.7V, 280mAh lithium-polymer cell replaces the original pack in the Sennheiser Flex 5000, Set 880, RS 5000, and RS 2000 wireless headsets. It matches OEM part numbers AHB571935PCT-03, BAP 800, and BAP-800. The cell fits the compact 37.50 × 20.00 × 6.20mm bay and connects to the same BMS circuit as the factory pack.

• Flex 5000, Set 880, RS 5000, and RS 2000 compatibility: These four models share a common receiver housing, connector pinout, and BMS handshake protocol — one cell fits all four without any modification to the dock or headset.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the RS 5000 base station. The BMS accepted the pack without error, the charging LED sequenced correctly, and the protection circuit tripped at the expected low-voltage threshold before recovery.
• First-cycle base station log: Charge the headset in the base station for a complete cycle before taking a call. DECT headsets log the new cell during this first charge — the talk-time estimate displayed on paired devices will not be accurate until that log completes.

Base station not recognising a new pack after swap

The Flex 5000 and Set 880 base stations communicate with the headset's BMS before displaying charge status. If the cell ships at storage voltage — typically around 3.6V — the BMS may not complete its handshake on the first dock. Place the headset in the base for at least 90 minutes without interruption. The charging indicator should cycle from amber to steady green once the BMS registers the new cell and the base logs the capacity profile.

Headset cuts out mid-call despite a full charge indicator

A 280mAh cell carries both audio decoding and the DECT radio transmitter simultaneously — the combined draw spikes during call setup and when the headset re-syncs with the base after brief range breaks. If the cell is in its first few cycles, internal resistance is still settling, and voltage can sag just enough to trip the BMS protection circuit. This clears after three to five full charge-discharge cycles as the cell stabilises. If cut-outs persist past cycle five, check that the base station contacts are clean and that the headset is seating fully — poor contact raises effective resistance and worsens voltage sag under load.