KEF Mu7 Replacement Battery 3.7V 750mAh Li-Polymer

KEF Mu7 — 3.7V Li-Polymer Replacement Battery (AHB603040P)

This 3.7V, 750mAh lithium-polymer cell replaces the original AHB603040P battery inside the KEF Mu7 wireless headphones. It powers both the active noise cancellation circuit and the Bluetooth radio simultaneously. Capacity matches the factory spec at 750mAh (2.78Wh).

• Mu7 platform fit: The Mu7 combines ANC processing with Bluetooth audio on a shared power rail. This cell meets that dual-load voltage requirement. The connector and physical dimensions — 42.20 x 29.80 x 6.00mm — match the original mounting cavity without modification.
• Bench tested on actual hardware: We cycled this cell under combined ANC and Bluetooth draw. The BMS handled the sustained dual-circuit load without triggering a premature cutoff. Charge acceptance matched rated capacity from the second cycle onward.
• First-cycle base station logging: Place the Mu7 on the charging base for a complete uninterrupted charge before first use. The headset's firmware uses that first cycle to register the new cell's capacity. Skipping this step causes the talk-time indicator to read inaccurately for several cycles.

Why the Mu7 cuts out mid-call on a new battery

The Mu7 draws from one cell to run Bluetooth transmission, ANC processing, and the audio drivers at the same time. Under that combined load, a cell at storage voltage — around 3.6V — can sag below the BMS cutoff threshold even if the indicator shows charge remaining. This is not a fault in the replacement cell. A full charge cycle before first use brings the resting voltage to 4.2V, which gives the BMS enough headroom to handle the peak draw without shutting down.

Talk time shorter than rated after fitting the replacement cell

Li-polymer cells do not deliver full rated capacity on the first charge cycle. Electrolyte wetting and electrode conditioning both improve over three to five full charge-discharge cycles. On the Mu7, this shows up as noticeably shorter listening sessions in the first week of use. Run three full cycles — charge to 4.2V, use until the low-battery warning, recharge — and rated capacity will stabilise.