I stumbled across this the other day, thought I would share it with my favorite forum browsers ^.^
Now, I have read two ways to do this. In one, you can put the tin foil on the negative ends and in another you can put it on the positive ends of the battery. I do not know which one works better.
1. Rip off a sheet of tinfoil to use to cover the end of the battery that you choose to.
2. Insert the battery along with the tinfoil to "fill the space"
Here is a picture of how it should look.
I DO NOT KNOW IF THIS IS DANGEROUS OR NOT. USE AT YOUR OWN RISK