About this replacement
Sennheiser HD 4.50BTNC / Momentum Series — 3.7V Li-Polymer Replacement Battery (AHB622540N1)
This 3.7V, 600mAh Li-Polymer cell replaces the internal battery in the Sennheiser HD 4.50BTNC, Urbanite XL, Momentum 2.0, and Momentum 3.0 wireless headphones. When the original cell degrades, Bluetooth range drops, active noise cancellation weakens, and charge cycles shorten noticeably. Swapping this cell restores the full power budget the headphones need to run both the APTX audio stack and the ANC circuit simultaneously.
- HD 4.50BTNC and Momentum platform fit: These models share a common internal power architecture — same 3.7V rail, same JST-style connector pinout, and a BMS that communicates state-of-charge to the firmware charge display. The cell dimensions (42.40 × 24.50 × 5.80mm) match the cavity across the full model range listed above.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the HD 4.50BTNC platform. The BMS accepted the new cell without error flags, the ANC circuit engaged normally at full draw, and the charge indicator tracked accurately after the first complete cycle.
- ANC load management on first use: The HD 4.50BTNC runs the noise cancellation processor and Bluetooth radio simultaneously — a combined draw the new cell needs one full charge cycle to calibrate against. Charge the headphones to 100% before the first extended listening session so the firmware sets an accurate state-of-charge baseline.
Why the HD 4.50BTNC cuts out mid-session on a new battery
The HD 4.50BTNC draws current from two circuits at once — the Bluetooth radio and the ANC microphone processor. At peak combined draw, voltage sag on a cell that hasn't completed its first conditioning cycle can dip below the BMS cutoff threshold, triggering an abrupt shutdown. This isn't a faulty cell — it's the protection circuit doing its job with a cell that hasn't yet reached stable internal resistance. Run two or three full charge-discharge cycles and the BMS recalibrates its cutoff window to the actual cell characteristics.
Headphones show full charge but cut off after short use
A replacement cell ships at storage voltage — typically around 3.6–3.7V — not at a calibrated full charge. The headphone firmware reads this as "full" but has no accurate capacity baseline yet. The result is a charge indicator that looks correct but drops suddenly under real load. Fix this by placing the headphones on charge until the indicator shows 100%, then running a full discharge before recharging again. After that first complete cycle, the state-of-charge display will track the actual cell capacity accurately.