Logitech UE Ultimate Replacement Battery 3.7V 3400mAh

Logitech UE Ultimate / UE MegaBoom 2 — 3.7V Li-ion Replacement Battery (533-000104)

This 3.7V 3400mAh Li-ion cell replaces the original battery in the Logitech UE Ultimate, UE MegaBoom 2, UE Kora Boom, and S-00122 portable Bluetooth speakers. It matches OEM part numbers 533-000104 and F12431581. Capacity figures come from the product data — 12.58Wh total.

• UE Ultimate and MegaBoom 2 platform fit: These models share the same 3.7V single-cell architecture, connector pinout, and BMS handshake protocol — one cell fits the full range without modification.
• Bench tested on actual hardware: We ran this cell through charge cycles on a UE MegaBoom 2 unit. The BMS accepted the cell without flagging an authentication error, and charge termination triggered correctly at 4.2V.
• Monthly discharge cycle for fuel gauge accuracy: For speakers used daily on a desk, let the cell drop below 20% at least once a month before recharging. Constant top-off charging without a full discharge causes fuel gauge drift — the indicator reads full while actual capacity has dropped significantly.

Capacity fade from constant desk-top charging on the UE Ultimate

Li-ion cells age fastest when held near full charge for extended periods. The UE Ultimate is commonly left plugged in on a desk, which keeps the cell sitting at 4.1–4.2V continuously. At that voltage, electrolyte oxidation accelerates and active material degrades faster than it would during normal charge-discharge cycling. Replacing the cell and changing the charging habit — unplugging once full — slows the next cycle of capacity loss.

Audio distorting before the battery indicator reaches empty

This happens when the cell voltage sags under the combined load of the amplifier and Bluetooth radio before the fuel gauge registers low. The amplifier clips because supply voltage drops below its operating threshold while the indicator still shows charge remaining. It is a voltage sag symptom, not a firmware fault. Check open-circuit cell voltage — if it reads below 3.5V under light load, the cell has lost internal resistance tolerance and needs replacing.