Several defibrillators, defibrillator architectures, defibrillator components and methods of operating defibrillators are described. In one aspect, a modular defibrillator architecture is described. A base unit provides a fully functional defibrillator. The functionality of the base unit can be supplemented by attaching an interface unit to the base unit or by connecting a smartphone the base unit. Such devices provide connectivity as well as a screen for displaying supplementary graphics and/or videos which are useful to support both emergency and maintenance & monitoring activities. In some embodiments a battery pack may also or alternatively be coupled to the base unit to prolong the unit's shelf life before recharging or replacement of its batteries is required. If necessary the base unit can be powered from a connected external device such as a mobile communication device.