A thermal battery including: a casing; a battery cell disposed in the casing; a heat generating pyrotechnic material, separate from the battery cell, at least partially surrounding the battery cell; and insulation disposed between the heat generating pyrotechnic material and the casing, wherein the heat generating pyrotechnic material is disposed in a flattened tube having a flat cross-section where at least two sides are substantially parallel, the flattened tube being spirally wound to form a shape corresponding to a complimentary shape of at least a portion of the battery cell.