US Patent 10361467 Power supply device

A first battery pack includes a first battery module and a first controller. A second battery pack includes a second battery module and a second controller. The first battery pack and the second battery pack are installed to be freely attachable and detachable in relation to a main body. An activation manager performs an activation instruction such that the first controller and the second controller do not activate at a same timing. The first controller which activates earlier operates in an ordinary mode in which power is supplied from the first battery module to an AC load. The second controller which activates later operates in a standby mode in which power is not supplied from the second battery module to the AC load.