About this replacement
Logitech Ultimate Ears Blast — 3.7V Li-ion Replacement Battery (T12367470JTZ)
This 3.7V 2600mAh (9.62Wh) Li-ion battery replaces the original cell in the Logitech Ultimate Ears Blast portable Bluetooth speaker. It fits models 984-000967, 1749LZ0PSAS8, and 884-000741. When the original cell degrades and the speaker no longer holds charge through a full listening session, this is the direct replacement.
- Ultimate Ears Blast compatibility: All listed model variants share the same 3.7V single-cell architecture, connector pinout, and BMS handshake. The replacement cell matches that voltage rail and passes the onboard fuel gauge initialisation without triggering a fault state.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the Blast platform, confirmed BMS acceptance at first connection, and verified the fuel gauge updated correctly across the full state-of-charge range without a stuck or false reading.
- Monthly discharge cycle on the Blast: Run the speaker down below 20% at least once a month before recharging. Constant top-off charging without a full discharge causes fuel gauge drift on this cell and accelerates capacity fade — the speaker will report full charge while actual usable capacity quietly shrinks.
Why the Blast reports full charge but audio cuts out after extended play
The Blast combines amplifier draw and Bluetooth radio draw on the same cell. Under sustained loud playback, the combined current pull causes voltage to sag faster than the fuel gauge recalculates. The BMS reads the sag as a low-voltage event and cuts output before the indicator reaches empty. Replacing a degraded cell — one with elevated internal resistance — eliminates the sag that triggers early cutoff.
Speaker won't respond to USB charging after sitting unused for months
If the Blast sat discharged for an extended period, the cell voltage can drop below the USB-C PD minimum acceptance threshold — typically under 2.5V on a 3.7V nominal cell. The charger handshake fails before any current flows into the battery. Connect the speaker to a 5V USB-A source first rather than a USB-C PD adapter, hold the power button for 10 seconds, then switch to the standard charger once the cell has recovered above the acceptance threshold.