QC20 battery won't charge after replacement

Thank you for finding that review, it was very helpful!

Quoting the review:

"I purchased this battery after my BOSE QC 20i indicated unchargeable battery (flashing red battery light) and the BOSE folks said they wouldn't fix it and would only give me a small credit toward the purchase of a replacement or upgrade QC product. After checking the web I learned how to open the QC 20i and what the inside looked like. After some delicate stripping of wires and soldering, the QC 20i worked fine again with this battery; but, it was also clear that the QC 20i charging of the battery still was inoperative (all lights green till the battery ran down and then flashing red again). That was taken care by spending about $20 for a small external charger, designed for this type of battery (sparkfun.com LiPo USB Charger). So, now, having spent a little over $30, my QC 20i has a new life, can be charged, and is good-to-go. Learning that Lithium Polymer batteries have a finite life of not too many years, irrespective of the number of use cycles, people should be cautious about purchasing expensive products where the battery can't be replaced, ether by the owner or the manufacturer. "

First measure the exact voltage of the original battery. Then drain the chargeg replacement under a suitable load until its voltage closely matches that of the old original battery. Your headphones will now charge.