Logitech Pure-Fi Anywhere 3.7V Replacement Battery NTA2479

Logitech Pure-Fi Anywhere / MM50 — 3.7V Li-ion Replacement Battery (NTA2479)

This is a 3.7V, 2200mAh Li-ion replacement battery for the Logitech Pure-Fi Anywhere Speaker 1st generation and MM50. It matches the OEM part number NTA2479. When the original cell loses capacity or stops holding charge, this swap restores cordless audio playback without replacing the whole unit.

• Pure-Fi Anywhere and MM50 compatibility: Both the Pure-Fi Anywhere 1st gen and MM50 use the same 3.7V single-cell architecture with the NTA2479 footprint. The PCB connector pinout and BMS handshake are identical across both models, so one cell fits both without modification.
• Bench tested on actual hardware: We cycled this battery through charge and discharge on the Pure-Fi Anywhere platform. The BMS accepted charge without fault flags, balanced correctly at 4.2V, and the protection circuit tripped cleanly at the low-voltage cutoff threshold before any cell stress occurred.
• Monthly discharge cycle for this speaker: The Pure-Fi Anywhere spends most of its life on a dock or desk, topped off continuously. Let the cell drain below 20% at least once a month before recharging — constant shallow top-off charging without a full discharge causes fuel gauge drift and accelerates capacity fade on this Li-ion cell.

Audio distortion before the battery indicator reaches empty on the Pure-Fi Anywhere

The Pure-Fi Anywhere's amplifier draws a sharp current spike at higher volumes. As the cell discharges toward its lower voltage range, internal resistance rises and the pack can no longer sustain that spike without voltage sag. The amplifier clips under the sag, producing audible distortion well before the battery indicator signals low. This is a cell health issue, not a speaker fault — a fresh cell with lower internal resistance holds voltage under load and eliminates the clipping.

Pure-Fi Anywhere won't wake from USB charge after sitting unused for months

A deeply discharged Li-ion cell can drop below the minimum acceptance voltage for the charging circuit — typically under 2.5V — and the USB charger refuses to initiate a charge cycle. The BMS blocks current to prevent damage to an over-discharged cell. To recover the pack, use a charger with a trickle or recovery mode that feeds a small pre-charge current until the cell climbs back above 2.8V, at which point the standard charge cycle will resume. If the cell does not respond above 2.8V after 10–15 minutes of recovery current, replace the battery.