A variety of arrangements and methods relating to a defibrillator are described. In one aspect of the invention, a defibrillator includes two paddles that each include a defibrillator electrode covered in a protective housing. The two paddles are sealed together using a releasable seal to form a paddle module such that the housings of the paddles form the exterior of the paddle module. An electrical system including at least a battery and a capacitor is electrically coupled with the paddles. The battery is arranged to charge the capacitor. The capacitor is arranged to apply a voltage at the defibrillator electrodes, which generates an electrical shock for arresting a cardiac arrhythmia.