Philips TAH9505BK Compatible Battery 3.7V 900mAh

Philips TAH9505BK — 3.7V Li-Polymer Replacement Battery

This 3.7V 900mAh Li-Polymer cell replaces the internal battery in the Philips TAH9505BK noise-cancelling wireless headphones. It restores charge capacity when the original cell has degraded from repeated shallow cycling. Capacity is 900mAh (3.33Wh) — identical to the factory specification.

• TAH9505BK fit: The TAH9505BK runs a single Li-Polymer cell at 3.7V nominal. This replacement matches the cell dimensions (39.50 × 33.60 × 6.70mm), voltage rail, and connector orientation, so the BMS accepts the new cell without throwing a charge fault.
• Bench tested on actual hardware: We cycled this cell through the TAH9505BK's charge circuit and confirmed the BMS completed a full charge handshake without error. The protection circuit tripped correctly at low-voltage cutoff — no false shutdowns under combined Bluetooth and audio draw.
• First-cycle calibration on the TAH9505BK: Seat the headset in its charging cradle and let it complete one uninterrupted full charge before use. The TAH9505BK's battery gauge resets its talk-time estimate during this cycle — skipping it means the indicator will read inaccurately for the first several uses.

Why the TAH9505BK cuts out mid-call even with charge showing

The TAH9505BK draws simultaneously from its audio amplifier and Bluetooth radio during a call. That combined load pulls more current than passive listening, which causes a momentary voltage sag on a degraded or newly installed cell. If the cell voltage dips below the BMS cutoff threshold — typically around 3.0V under load — the headset shuts off even though the resting charge level looked fine. A new cell at full charge resolves the sag. After a full first cycle, the protection circuit holds stable under combined draw.

Base station shows full charge but headset cuts off after short use

A replacement cell ships at storage voltage — usually between 3.6V and 3.8V — not at a full 4.2V. The TAH9505BK base station can misread this as a complete charge and stop topping up the cell. The result is a headset that appears fully charged but carries only partial capacity. Place the headset in the cradle, wait for the charge indicator to cycle through a complete charge sequence from scratch, and verify the cell reaches 4.2V before first use.