Logitech 533-000146 Replacement Battery 7.4V 3400mAh

Logitech Ultimate Ears Megaboom 3 — 7.4V Li-ion Replacement Battery (533-000146)

This 7.4V, 3400mAh Li-ion battery replaces the OEM pack in the Logitech Ultimate Ears Megaboom 3 and fits models 984-001362 and 084-000845. It matches the original voltage rail and connector, so no modifications are needed. Use it when the factory battery no longer holds charge or the speaker stops powering on.

• Megaboom 3 platform fit: The 984-001362 and 084-000845 share the same battery bay geometry, connector pinout, and BMS handshake protocol. One replacement covers both hardware revisions without adapter cables or firmware workarounds.
• Bench tested on actual hardware: We cycled this pack through full charge and discharge on a Megaboom 3 unit. The BMS accepted the cell without fault flags, voltage held within spec across the amplifier and Bluetooth radio draw, and the onboard fuel gauge tracked correctly from 100% to cutoff.
• Monthly discharge cycle for Megaboom 3: If you leave this speaker plugged in or top it off before it drops below 50%, the fuel gauge drifts over time. Let it drain below 20% at least once a month before recharging — this keeps the coulomb counter accurate and slows cell degradation at the high end of the charge curve.

Audio distorting before the battery indicator reaches empty

As a Li-ion cell ages or sits deeply discharged, its internal resistance rises. Under the combined current draw of the amplifier and Bluetooth radio at moderate-to-high volume, terminal voltage sags below what the amp stage needs — even if the indicator still shows one or two bars. The amplifier clips because it can't sustain clean output at that voltage, which shows up as crackling or distortion before any low-battery warning appears. A fresh cell with lower internal resistance eliminates the sag; terminal voltage should stay above 7.0V under load at the Megaboom 3's rated output.

Speaker shows full charge indicator but audio cuts after an hour

This is fuel gauge drift — common when a pack has been shallow-cycled for months without a full discharge. The onboard gauge loses calibration and reports a higher state of charge than the cell actually holds. The cell hits real cutoff voltage while the indicator still reads high, and the speaker shuts down. To recalibrate, run the speaker to complete shutdown, then charge uninterrupted to 100% in one session. If the problem persists after two recalibration cycles, the cell itself has lost capacity and needs replacement.