Next I needed a backing to hold the LED and battery in, I also wanted to be able to remove it to change the battery when it died. I found a small badge, that was the right size and used the badge shell for the backing. I used some Sugru to form a seal around the back of the button to hold the shell on. I took off the shell while the Sugru was curing so that it didn't become permanently attached. Once cured it created a snug fit holding the backing in place and it can be removed with a screwdriver or your fingernail when you need to change the battery.