Nerf Rival Khaos Internals Question (capacitor?)

Hello, I modified the Nerf Rival Khaos to be controlled with a switching circuit and I ripped out the internals of the weapon. However, when the program isn't running, the capacitor that is connected to the battery is getting extremely hot. I'm thinking it is a capacitor, but not 100% sure. This capacitor only gets warm with the program running, but instantly starts to burn up once the program is idle. Any idea on how to fix this problem? Thank you! Here is a picture of what I'm talking about.