Battery door is missing - QuietComfort® 2 Acoustic Noise Cancelling® headphones
Amazon.com: 750mAh Replacement Battery for Bose QC35 QC45 QuietComfort 35 II Wireless Headphones, Compatible with Sony WF-1000XM3 WF-SP900 Charging Case Battery : Health & Household
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Bose QC25 Limited Edition headphones review: Excels in the sound department - Times of India