About this replacement
Marshall Middleton — 11.1V Li-ion Replacement Battery (C406A1)
This is an 11.1V, 2600mAh Li-ion replacement battery for the Marshall Middleton portable Bluetooth speaker. It fits the Middleton housing directly, restoring full power to the speaker's amplifier, Bluetooth radio, and onboard electronics. Use Capacity from product data: 2600mAh / 28.86Wh.
- Middleton platform fit: The Middleton runs its Class D amplifier and Bluetooth 5.2 radio from a single 11.1V three-cell pack. This replacement matches that voltage rail and carries the same connector and BMS handshake the speaker's charge management circuit expects — no firmware rejection on connection.
- Bench tested on actual hardware: We cycled this pack through the Middleton's charge IC at full volume output. The BMS held charge termination cleanly at 12.6V and triggered low-voltage cutoff before cell voltage dropped below safe floor — no runaway, no false full-charge flag.
- Fuel gauge reset after install: The Middleton's onboard gauge IC tracks coulombs from the original cell. After fitting a new pack, run one full charge to 100%, then play until the speaker shuts off on its own — this resets the gauge baseline so the indicator reads accurately rather than reporting phantom capacity.
Why the Middleton shows full charge but audio drops after extended play
The Middleton's charge indicator reads state-of-charge from a coulomb counter, not direct cell voltage. When the original battery degrades, the counter's baseline drifts — the speaker reports 100% while actual usable capacity is a fraction of that. Under amplifier load, cell voltage sags faster than the counter expects, and the BMS trips the output before the indicator reaches empty. Fitting a new 2600mAh cell and running the gauge reset cycle described above corrects the mismatch.
Audio distorting before the battery indicator reaches empty
At high volume the Middleton's amplifier pulls peak current that causes the pack's terminal voltage to sag temporarily below the amplifier's rail requirement. The amp clips — output distorts — even though the battery still holds charge. This is voltage sag under load, not capacity failure. If it happens on a new pack, check that the cell connections are seated fully; a partial contact adds resistance and worsens sag. A healthy, fully charged 11.1V cell should sustain the load without sag until terminal voltage falls below 9.9V under draw.