Ok so you need some watch batteries in a hurry and cant find any on the shelf? well if its the smaller thin ones your looking for then grap one of the small 12 volt batteries that go in some cameras, and my multimeter :P, so anyway now the part that comes with a disclaimer, (dont do this unless your sure, cells are dangerous if they rupture) get a file and file the end cap from the positve terminal untill it comes out , you may need to use a set of pliers or a screwdriver to lever it out once the metel case is open. Now tip up the power cell and if you have to, pry the edge where the metel case has a seam, untill the eight cells in the battery fall out.
So now you have some power for your next led throwie project which can be found over at instructables.com. Or if you need to reverse this to get a 12volt cell for the camera dlash that went flat, well grap a cheap set of watch batt's and tape eight together to form the stacked cell, then place a small magnet from a old cd drive to the end as a positive terminla and there you go,
Remember, dont play with cells that rupture or show signs of swelling, and please wear safety glasses for this one.