An onboard battery for a vehicle includes battery modules each including battery cells, an auxiliary device for charging, and a housing case housing the battery modules and auxiliary device. Cooling air is taken from air intake holes into the battery modules to cool the battery cells. A middle of a transversal direction of the battery modules is shifted to either left or right of a center of a transversal direction of a vehicle. The auxiliary device is disposed at an other end portion in the transversal direction. Each air intake hole is between a left and right end of each battery module and in a back of each battery module. A side opposite to a side of the auxiliary device has an air introducing port 55a that takes cooling air into the housing case.