A miniature electrochemical cell having a volume of less than 0.5 cc includes a casing having a header assembly comprising a ceramic plate formed by co-firing a metallic-containing paste in first and second via holes extending through a green-state ceramic. The ceramic plate is joined to a metal ring by a gold-braze to form the header assembly that is secured to an open-ended metal container by a weld to provide the casing. The fill material resulting from sintering the metallic-containing paste provides a first conductive pathway to the anode current collector contacting an anode active material and a second conductive pathway to a cathode current collector contacting a cathode active material. A solid electrolyte activates the anode and cathode while also serving as a separator. Outer surfaces of the first and second conductive pathways are configured for electrical connection to a load.