The are also detachable so they can be replaced if needed. Very cozy and warm Id had to put about 20-30 hours in. As for the battery acid odor, I cant really think of the cause of this. If I have any channel imbalance it should only be at low volumes. Even my stereo speakers dont give me the quality sound this does. Very quiet headphones. I wear a size 13 with a wide foot, and got a size 13 in these. She said they cant change the insoles out, but the next replacement pair also has a 90 day quality guarantee on them so if I continue to have the same problem theyll continue replacing them. Nothing much there.