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.