My dad has a special Zippo flashlight from his company's 50th anniversary. It stopped working a while ago, and after contacting Zippo, found out the Ziplights have been discontinued.
With nothing left to lose, he let me open it and try and fix it. Opening it was surprisingly easy. The two halves are not glued, melted or sealed together. They just pop open.
The two batteries inside are very skinny. Much smaller than AAA. But I figured I'd seen them somewhere before. Sure enough - there's 6 of them in a regular 9V battery.
After cleaning the contacts and replacing the batteries, it works again!