Capacitor. This device is designed to store and release electric charge. It can release its charge faster than a battery, but unlike a battery it cannot produce electricity but can only store it. Capacitors store their charge on two metal plates (here rolled up in a cylinder shape) separated by a dielectric (non-conducting material). Connection to an electric current will charge the capacitor. Connection to circuit without a battery will then discharge it, to power a camera flash for example. This is a 2200 microfarad electrolytic capacitor, a few centimetres long. It has a breakdown voltage of 25 volts.