This is the battery door for an MP3 audio player I have. The "V"-shaped catch on the battery door has lost its spring-like quality and the battery door sometimes falls off of the player. I tried heating the bottom of the "V" and bending the catch, but the plastic is weak and it does not hold its position.
Step 1: Open the catch a bit
I pulled the catch open to spread the "V" so it will hold itself into the player if this position could be maintained. Be careful not to break the plastic by pulling too much.
Step 2: Test for thickness
I folded a new rubber band over and stuffed it into the "V" to see how many layers of rubber band I would need to fill the "V." Two should do the job if I can get them to stay in the lower portion of the "V" opening on the catch. Do not use an old rubber band. Those have already lost some of their elasticity.
Step 3: Cut the rubber band
I cut two pieces of rubber band as long each as the catch is wide.
Step 4: Glue the rubber pieces in place
I glued each piece of rubber to the plastic surface it touches, but did not glue them to each other. I used a fast setting epoxy glue and a toothpick. I tried to push the pieces of rubber as far as possible down into the "V" opening of the catch. Wait for the glue to set.
Step 5: Finished
My battery door once again closes with a reassuring "click," and it stays in place.