Sennheiser PXC 550 Replacement Battery 3.7V 650mAh

Sennheiser PXC 550 / MB 660 / EPOS ADAPT 660 — 3.7V Li-Polymer Replacement Battery (AHB413645PCT)

This is a 3.7V, 650mAh Li-Polymer replacement battery for the Sennheiser PXC 550, MB 660, and EPOS ADAPT 660 wireless headsets. It fits all three models directly — same flat-cell form factor, same connector, same BMS communication profile. Replace it when your headset stops holding charge or cuts out during use.

• PXC 550, MB 660, and ADAPT 660 share this cell: All three headsets use the same flat Li-Polymer cell and internal BMS handshake protocol. The connector pinout, physical dimensions (45.44 × 33.84 × 4.30mm), and protection circuit are identical across the platform — one cell fits all three.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the PXC 550. The BMS handshake completed cleanly, protection circuit tripped correctly at low-voltage threshold, and the base station accepted the pack without an error flag.
• Base station first-cycle logging: Dock the headset in the base station and allow a full uninterrupted charge before your first call. DECT headsets log the new cell during this cycle — without it, the base unit's talk-time estimate will read inaccurately for the first several uses.

Why the PXC 550 cuts out mid-call even with a new battery

The PXC 550 runs active noise cancellation and a DECT radio simultaneously. That combined draw creates brief current spikes that a degraded or partially charged new cell may not sustain. The BMS reads the voltage dip as a low-cell condition and trips, cutting audio. A full first charge cycle before use brings the cell to its working voltage range and eliminates most mid-call dropout on a fresh replacement.

Base station shows full charge but headset shuts off after a few minutes

A new Li-Polymer cell ships at storage voltage — typically around 3.6–3.7V — not at full charge capacity. The base station LED can show "charged" before the cell has actually completed a full cycle. The headset then draws down quickly because the cell hasn't been conditioned. Dock the headset for a complete uninterrupted charge cycle; after 3–5 full cycles, talk time stabilises at rated capacity.