Automated external defibrillator with a plurality of power sources

An automated or semi-automated external defibrillator (AED) is provided with a plurality of power sources. The AED includes a first power source that powers circuitry creating a defibrillation electrical shock, and a second power source for powering other circuitry. By including a separate power source for the low-power needs of the AED, the high-power source will typically last longer than if the low-power source were omitted. This reduces maintenance costs, particularly where the high-power source is more expensive to replace than the low-power source. Furthermore, one may use the high-power source as a backup to the low-power source so the AED can still operate even if the low-power source fails.