a battery stack in which a plurality of battery cells are stacked, each of the plurality of battery cells including a gas discharge valve on a top surface of the each of the plurality of battery cells, and the gas discharge valve opening when an internal pressure of an outer covering can of the each of the plurality of battery cells increases, the gas discharge valve disposed at a top surface of the battery stack;

a first cover provided on the top surface of the battery stack and defining a first gas duct that communicates with the gas discharge valve of each of the plurality of battery cells; and

a second cover provided on a top surface of the first cover and defining a second gas duct on a top surface of the first gas duct,

wherein a plurality of communication holes that communicate the first gas duct and the second gas duct are disposed on the top surface of the first cover,

wherein the first gas duct has a first gas exhaust port, and the second gas duct has a plurality of second gas exhaust ports separate from the first gas exhaust port, each of the first gas exhaust port and the plurality of the second gas exhaust ports individually open to an outside of the power supply device,

wherein the first gas duct and the second gas duct are configured to individually discharge gas from the gas discharge valve to the outside of the power supply device via a corresponding one of the first gas exhaust port and the plurality of the second gas exhaust ports, respectively,

wherein the first cover includes a communication rib protruding toward the second cover around each of the plurality of communication holes, and

wherein the first cover includes a partition rib that partitions between adjacent ones of the plurality of communication holes so as to form partitioned spaces, and one of the plurality of the second gas exhaust ports provided at each of the partitioned spaces.