A possibility of it not charging could be that you still have inflammation from the surgery and the signals can't connect. I heal very slowly and for the first couple of months I had a hard time recharging due to the ongoing swelling/inflammation. I found a wierd position where the signal did connect and for quite a while had to keep it in that position. I had to lay a certain way and my husband taped the heck out of it to keep it in place but it finally did charge. Just make sure you shave first as I lost a lot of hair when he pulled all that tape off