An inertial igniter for igniting a thermal battery upon a predetermined acceleration event. The inertial igniter including: a base having a first projection; a striker mass rotatably connected to the base through a rotatable connection, the base having a second projection aligned with the first projection such that when the striker mass is rotated towards the base, the first projection impacts the second projection; a rotation prevention mechanism for preventing impact of the first and second projections unless the predetermined acceleration event is experienced; and a spring for biasing the striker mass in a biasing direction away from the base, the spring being disposed between a portion of the striker mass and a portion of the rotation prevention mechanism.