My battery does not seem to be making contact inside the headphones

I had the issue with a pair in which the battery had been left during storage. As often happens with those copper-colored batteries, it leaked. I was able to apply a few drops of white vinegar to the spring and spring holder in the little door to the compartment, then rinse and repeat without getting liquid inside the headphones. I also used an emery board to brighten the part of the spring that contacts the battery. Again, don't get dust inside. Even though you cleaned it, there could be a little bit of corrosion where the spring is held in place or where the electricity flows into the headset, or on the tip of the spring. I put in a new battery and they worked!