About this replacement
Sennheiser Momentum TW2 Charging Case — 3.7V Li-ion Replacement Battery (14500CY-900)
This 3.7V 700mAh Li-ion cell replaces the internal battery in the Sennheiser Momentum TW2 charging case. The case battery is what stores charge between wall outlet sessions and delivers it to the earbuds — when it degrades, the earbuds stop getting topped up mid-day. This replacement restores that between-charge buffer.
- Momentum TW2 case fit: The TW2 case uses a single cylindrical Li-ion cell rated at 3.7V to run its internal charge management circuit. The 14500CY-900 format matches the cell footprint, contact orientation, and voltage rail the case's charging IC expects.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the TW2 case platform. The onboard BMS accepted the new cell without error, completed a full charge cycle from depleted, and passed charge through to connected earbuds at the correct output voltage.
- First-cycle case conditioning: After fitting this cell, charge the case fully from empty before loading the earbuds. The TW2 case charge controller recalibrates its capacity estimate on the first full cycle — skipping this step causes the LED indicator to report inaccurate charge state for the first several uses.
Why the TW2 case LED shows full but earbuds go flat after one top-up
The TW2 case measures its battery state by tracking voltage, not a coulomb counter. A new cell installed at storage voltage — typically around 3.6V — sits close enough to nominal that the case reports full. But the usable capacity window only unlocks after a complete charge-discharge cycle drives the cell through its full voltage range. Until that first full cycle runs, the case pulls charge from a narrow voltage band and exhausts it faster than the indicator suggests.
Case charging stops early and the amber light pulses without reaching solid white
This symptom usually means the charge IC timed out before the cell reached termination voltage. It happens when a degraded or deeply discharged cell takes longer than the case's charge timer allows. With a fresh replacement cell starting from storage voltage, plug the case into the charger and leave it connected for a minimum of two hours without interruption. If the pulsing persists past that point, check the USB cable and source — the TW2 case requires a stable 5V input; underpowered sources cause the charge controller to abort early. Confirm input voltage is at 5.0V before suspecting the cell.