A highly compact electrochemical cell comprised of a casing having a proximal opening, a distal opening, and an intermediate sidewall surrounding an enclosed volume. A glass-to-metal seal is disposed in the proximal opening and within the enclosed volume of the casing, and a terminal pin extends from outside the casing through the glass-to-metal seal into the enclosed casing volume. An insulator is disposed along the casing sidewall. A cathode is contained within the insulator in electrical contact with the terminal pin. A separator disc is disposed contiguously with the casing sidewall and in contact with the cathode. An anode is provided in contact with the separator disc and with the casing sidewall opposite the cathode. An electrolyte is provided within the cell, and a lid is sealed to the casing to hermetically enclose the cell contents.