Is the lithium ion battery user replaceable?
I would prefer to replace it myself as opposed to sending my headphones away.
I do not believe it is. But I have had no problems with Bose replacing the device if the battery fails. It's rare but I have had some eventually go bad. Just had to call Bose and tell them and they RMA it and sent me a new one every time. They are good at standing behind the products they sell.