A battery module is disclosed having a plurality of battery cells and internal relay controllably coupled to an internal module controller, said controller having a plurality of programmed states. Transitions between programmed states are disclosed responsive to a secure command message, and responsive to a monitored operating condition. Passive and active states are disclosed. A modular battery pack is disclosed consisting of a plurality of modules connected in parallel, which can be individually and independently activated and deactivated responsive to a secure command message. Methods are provided for authentication of command messages and for authentication of the command message source.