You can only share a Badge with another Teacher when you are creating a new Badge. When creating a new Badge, you can choose to share that Badge by ticking the “Share this Badge with other teachers” box at the bottom of the "Create a new Badge" pop up.
Other Teachers will then be able to access and use your Badge.
Note: You must check the box to share the Badge with other Teachers when you create the Badge. You will not be able to go back later to share it.