An onboard battery includes an accommodation case that has an upper accommodation unit and a lower accommodation unit positioned below the upper accommodation unit battery modules each having battery cells, and joints that couple the upper accommodation unit and the lower accommodation unit to each other. At least one battery module is accommodated in each of the upper accommodation unit and the lower accommodation unit. When a predetermined load or more is applied to the upper accommodation unit, a stress acts on the joints such that the upper accommodation unit and the lower accommodation unit are separated from each other, and the upper accommodation unit is moved away from the lower accommodation unit.