About this replacement
Logitech Pure-Fi Anywhere Speaker 2nd MM50 — 3.7V Li-ion Replacement Battery (NTA2335)
This 3.7V, 3000mAh Li-ion cell replaces the NTA2335 battery in the Logitech Pure-Fi Anywhere Speaker 2nd MM50. It restores wireless audio playback when the original cell no longer holds charge. Dimensions are 65.77 × 20.18 × 18.38mm — verify against your existing cell before ordering.
- Pure-Fi MM50 fitment: The MM50 runs a single-cell 3.7V pack with a protection circuit that monitors cell voltage and temperature. This replacement matches the original NTA2335 connector pinout and BMS communication so the speaker's charge indicator reads correctly from first cycle.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the MM50 platform. The onboard BMS accepted the cell without fault codes, and the protection circuit tripped correctly at the low-voltage cutoff threshold.
- Fuel gauge calibration on the MM50: Once a month, let the speaker discharge below 20% before plugging in. The MM50 uses a Coulomb-counting gauge that drifts when the cell is constantly topped off from high states of charge — a full discharge cycle re-anchors the gauge and slows capacity fade on the Li-ion cell.
Bluetooth dropping at high volume on the MM50
At loud output levels, the MM50's amplifier draws a sharp current spike on top of the Bluetooth radio's steady draw. If the cell has any internal resistance — from age or shallow cycling — voltage sags under that combined load. The BMS interprets the sag as a near-empty cell and briefly cuts radio power to protect the pack. Replacing the cell with a fresh 3000mAh unit restores the headroom needed to sustain both draws simultaneously.
Audio distorting before the battery indicator reaches empty
This happens when the cell's actual voltage drops faster than the fuel gauge tracks it. The amplifier begins clipping once supply voltage falls below the threshold it needs for clean output — but the indicator still shows one or two bars. A degraded cell causes this gap to widen over time. Replacing the NTA2335 cell and running one full discharge cycle to below 3.0V at the terminals re-synchronises the gauge with actual cell state.