An onboard battery includes an accommodation case that has a hollow cross section formed with multiple cavities 9a, and at least one battery module that has at least one battery cell and is accommodated in the accommodation case. At least one disposition depression that communicates with one of the multiple cavities and is opened upward is formed in a portion positioned below the at least one battery module in the accommodation case, and at least one heater that heats the at least one battery cell is disposed in the at least one disposition depression so as not to be in contact with the at least one battery cell.