Abstract: An over-voltage protection device (51) for a secondary battery is disclosed which includes an outer casing (52) with plastic cover (53), terminals (56, 57, 58) and a piezoelectric actuator (54). Piezoelectric actuator (54) has first and second electrodes which are electrically connected to terminals (56, 57) respectively. Terminal (58) has a stationary electrical contact (60) mounted therein. The piezoelectric actuator (54) is cantilever mounted within casing (52) with a movable contact (61) mounted on its distal end that is positioned to be in engagement with stationary contact (60). When an over-voltage is applied between terminals (56, 57), it causes a displacement of the distal end of piezoelectric actuator (54) and correspondingly of the disengagement of movable contact (61) from stationary contact (60).