I had the exact same problem with my Bose QC15s. I was on a transatlantic flight and I changed the battery only to find out that the headphones would not power up. I thought it was the battery and changed at least 3 batteries. I then read this very valuable post, went downstairs to the kitchen and poured some turpentine at the end of an earbud. I then swivelled it along the positive terminal contact point to remove some dirt. And Voila!! Now they work perfectly. Thank you all so much.