NOVELTY - Vehicle (I) (10) comprises: battery housing (22) in selective fluid communication with cabin of vehicle (14); traction battery (12) disposed within housing; accessory battery; engine; closeable barrier (26) system electrically connected with accessory battery and configured to fluidly isolate battery housing from cabin when closed; and at least one controller configured to, in response to trigger condition, disable traction battery and increase output of accessory battery to close barrier system to isolate gas in battery housing from cabin.    USE - Used as vehicle.    DETAILED DESCRIPTION - Vehicle (I) (10) comprises: a battery housing (22) in selective fluid communication with a cabin of the vehicle (14); a traction battery (12) disposed within the housing; an accessory battery; an engine; a closeable barrier (26) system electrically connected with the accessory battery and configured to fluidly isolate the battery housing from the cabin when closed; and at least one controller configured to, in response to a trigger condition, disable the traction battery and increase an output of the accessory battery to close the barrier system to isolate gas in the battery housing from the cabin, where the controller is further configured to, in response to the trigger condition, increase torque output of the engine to satisfy driver torque demands. INDEPENDENT CLAIMS are also included for:    (1) a vehicle (II) comprising a traction battery, a traction battery housing surrounding the traction battery and in selective fluid communication with a cabin of the vehicle, the door system electrically powered by an accessory battery and operable to selectively isolate the battery housing from a cabin compartment of the vehicle, and the conduit fluidly connecting the traction battery housing to the cabin, where the door system includes a door arranged such that the door is at least partially disposed outside of the conduit when the door system is open; and    (2) controlling the vehicle comprising in response to a fault condition, (i) disabling the traction battery, (ii) closing the barrier system electrically powered by an accessory battery such that the housing surrounding the traction battery is fluidly isolated from the cabin of the vehicle, and (iii) activating the engine to satisfy driver torque demands.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a portion of a powertrain and a battery ventilation system.    Vehicle (10)    Traction battery (12)    Vehicle cabin (14)    Battery housing (22)    Barrier (26)