BATTERY PACK

A controller makes it possible to more securely execute, when a thermal runaway occurs in a battery pack, communications for a fail-safe action with an external device. A controller is configured to execute, when a thermal runaway occurs in a battery pack, communications for a fail-safe action with an external device. A first battery module is arranged on a side farther than the controller in a first direction. A second battery module is arranged on a side farther than the controller in a second direction that is a direction opposite to the first direction. A first wire extends from the controller in the first direction and passes immediately above the first battery module. A second wire extends from the controller in the second direction and passes immediately above the second battery module, and has a function identical to a function of the first wire in the communications.