An external defibrillator comprising: a unit for providing electrical stimulation of a patient; a battery module that includes: a battery housing; a plurality of battery banks within the housing, each of the battery banks being electrically isolated from each of the other battery banks within the housing and having a total lithium content of less than an amount requiring special handling procedures during transportation and storage; and a plurality of pairs of electrical contacts external to the housing, each of the pairs of electrical contacts being configured to provide an electrical connection to an associated battery bank; and a connector unit external to the battery housing that includes: a plurality of pairs of electrical contacts configured to mate with the plurality of pairs of electrical contacts of the battery module; and circuitry electrically connecting the plurality of pairs of electrical contacts of the connector unit to provide a single voltage output to the unit for providing electrical stimulation.