Bose QuietComfort 20 Replacement Battery 3.7V 240mAh

Bose QuietComfort 20 — 3.7V Li-Polymer Replacement Battery (PR-452035)

This 3.7V 240mAh lithium-polymer cell replaces the original PR-452035 battery in the Bose QuietComfort 20 (QC20) in-ear headphones. It powers both the active noise cancellation circuit and audio playback. When the original cell degrades, ANC weakens or drops out entirely before the audio does — this replacement restores both functions.

• QuietComfort 20 and QC20 fit: Both model names refer to the same hardware revision. They share the same battery footprint at 36.30 × 20.20 × 4.60mm, the same 3.7V nominal rail, and the same PR-452035 part number. No adapter or modification needed.
• Bench tested on actual hardware: We cycled this cell through the QC20 ANC circuit under combined noise-cancellation and audio load. The BMS held within the expected charge and discharge cutoff thresholds, and the ANC module received stable voltage throughout the draw cycle.
• ANC module charging tip: The QC20's noise-cancellation circuit draws current even when the headphones are not playing audio. If the battery sits discharged for weeks, charge the unit fully via the Lightning or micro-USB port before switching ANC on — powering the ANC circuit from a deeply discharged cell can cause the module to reset mid-use on the first session.

Why ANC cuts out before audio does on a degraded QC20 battery

The QC20 runs two separate draws from the same cell: the audio path and the active noise-cancellation DSP. The ANC circuit has a higher minimum operating voltage than the audio path. As the cell ages and internal resistance rises, voltage sag under combined load drops the supply below the ANC threshold first — audio keeps playing but noise cancellation shuts off. A fresh cell with lower internal resistance maintains voltage above both thresholds across the full discharge curve.

ANC indicator light stays on but noise cancellation feels weak after replacement

This happens when a new cell is installed at storage voltage — typically around 3.6V — rather than after a full charge cycle. The ANC module powers on but the DSP cannot sustain full processing depth without a stable voltage above 3.7V. Charge the QC20 to 100% before the first use. If the symptom persists after a full charge, check that the battery contacts inside the housing are clean and making firm contact with the cell terminals.