About this replacement
Marshall Middleton — 11.1V Li-ion Replacement Battery (C406A7)
This is an 11.1V, 3350mAh Li-ion battery for the Marshall Middleton portable Bluetooth speaker. It replaces OEM part numbers C406A7 and C406A1. Fit the new cell when the original no longer holds a charge or shuts down mid-session.
- Middleton-specific fit: The Middleton runs a three-cell Li-ion pack at 11.1V nominal to feed its Class-D amplifier and Bluetooth radio simultaneously. Both C406A7 and C406A1 share the same voltage rail, connector, and BMS handshake, so this replacement works across both OEM revisions.
- Bench tested on actual hardware: We cycled this cell through the Middleton's full charge and discharge sequence. The BMS communicated correctly with the speaker's fuel gauge, and charge termination triggered cleanly at capacity — no false-full cutoffs observed.
- Monthly discharge cycle for the Middleton: The Middleton is commonly left on a desk and topped off before it drops below 50%. Doing that consistently causes fuel gauge drift on the Li-ion cell. Let the speaker discharge below 20% at least once a month before plugging in — this keeps the gauge calibrated and slows capacity fade.
Why the Middleton distorts audio before the battery indicator reaches empty
At high volume, the Class-D amplifier draws sharp current spikes. As the cell ages and internal resistance rises, those spikes cause voltage sag — the pack momentarily dips below the amplifier's clean-operation threshold even though the fuel gauge still reads 20–30%. The amplifier clips because it can't sustain the supply voltage under load, not because it's faulty. Fitting a fresh cell with lower internal resistance eliminates the sag and restores clean output down to true low-battery levels.
USB-C not waking the Middleton after leaving it stored for months
Li-ion cells self-discharge slowly during storage. If the Middleton sits unused for several months, the pack can drop below the USB-C PD minimum acceptance voltage — typically around 2.5V per cell — and the charger won't negotiate a connection. The speaker appears completely dead even on a working cable. Try a 5V 500mA USB-A to USB-C cable first; some chargers will trickle current at low voltage where PD won't. If the pack fails to recover after 30 minutes at trickle, the cell is below recovery threshold and needs replacement.