Logitech UE Boom 2 Replacement Battery 3.7V 3400mAh

Logitech UE Boom 2 — 3.7V Li-ion Replacement Battery (00798-601-8207)

This 3.7V, 3400mAh Li-ion cell is a direct replacement for the UE Boom 2 and UE Boom 2 Ultimate portable Bluetooth speakers. The original battery degrades after repeated charge cycles, causing shortened playtime and unreliable audio output. Swapping this cell restores the speaker's full charge capacity at the correct voltage the amplifier and Bluetooth radio expect.

• UE Boom 2 and UE Boom 2 Ultimate compatibility: Both models share the same cylindrical cell format, connector pinout, and BMS handshake protocol. The fuel gauge IC in the speaker reads cell state-of-charge directly, so correct capacity at 3400mAh is required for accurate indicator behaviour.
• Bench tested on actual hardware: We ran this cell in a UE Boom 2 unit and confirmed the BMS accepted the pack without fault codes, the fuel gauge calibrated correctly on first full charge cycle, and the amplifier draw did not trigger premature BMS cutoff at high volume.
• Monthly discharge cycle for UE Boom 2 users: Let the speaker drain below 20% at least once a month before recharging. Constant top-off charging — plugging in at 60% or 70% repeatedly — causes fuel gauge drift and accelerates capacity fade on this Li-ion cell.

Audio distorting before the battery indicator reaches empty

As a Li-ion cell ages, its internal resistance rises. Under the combined load of the amplifier and Bluetooth radio, voltage sag pulls the cell below the amplifier's clean-power threshold before the fuel gauge reads zero. The amplifier clips because it cannot sustain output at the sagged voltage, and the result is audible distortion at mid-to-high volume levels. Replacing the cell removes the high internal resistance and restores stable voltage delivery under load — distortion at normal playback levels should stop.

Speaker not waking from USB charge after sitting unused for weeks

A deeply discharged Li-ion cell can fall below the minimum voltage USB charging circuits will accept — typically around 2.5V for this cell chemistry. When that happens, the speaker's charge management IC refuses to begin a charge cycle, and the unit appears completely dead. Connect the speaker to a 5V USB source and leave it for 20–30 minutes without pressing any button — some charge controllers run a low-current trickle recovery mode that slowly brings the cell back above the acceptance threshold. If the indicator LED still does not light after 45 minutes, the cell has fallen too low to recover and requires replacement.