A safety device (1) for a lithium electrochemical generator battery, including a box (100), configured to house a plurality of lithium electrochemical generators; a cover (200) arranged gas-tightly on the opening (130) of the box; an opening (120) forming a vent situated in one of the walls of the box (100) or situated in the cover (200); a conduit (300) having two openings (311, 312) where one of the openings (311) is gas-tightly connected to the opening (120) forming a vent of the box; a covering part (400) positioned gas-tightly at an opening of a wall of the compartment and the second opening (312) of the conduit, and where said covering part comprises a portion (410) adapted to tear at a threshold pressure Ps; where the walls of the box, the cover, the conduit and the covering part are secured to each other so as to ensure sealing against the gases up to a pressure above the threshold pressure Ps.