I have fixed the button before. Attach a Carto or atty like you normally would. Hold the battery in one hand, and with your other hand on the carto/atty, with your fingers placed on the silver piece that holds the button. Carefully wiggle it back and forth while also gently pulling. You will see the silver piece slowly separate from the battery. Be careful not to let the piece come off too roughly because the wires are very fragile. Once the silver piece is disconnected from the battery body, you can manipulate it to allow the plastic button to fall out. Yours may be chipped or dislodged. The button needs to go back in a certain way, because one edge of it is flat and has a designated area in which to lie (at least my genuine twist did). You have to fiddle with it with the hole facing downward so gravity brings the button down into its hole. The hard part comes when you go to reattach it, because the plastic button has to shimmy over the circuit board perfectly. Just keep trying.
