An electrochemical source that provides electrical power to a downhole or surface tool used for determining the location or assisting in the extraction of hydrocarbons. Unlike a conventional battery, an oilfield battery must safely provide power sufficient to enable a tool to perform as specified, even on extended jobs. Designed with rugged external packaging to fit within a confined tool space, it must tolerate extreme temperatures while withstanding high shock and vibration. Its internal chemistry must also accommodate a long shelf life.