In one embodiment, the invention includes a power source having a plurality of battery groups and a processor coupled to the groups and adapted to electrically disconnect a group from the power source. Each group includes a plurality of cells, a sensor adapted to sense operating parameters of the cells, and a protection circuit coupled to the sensor. In another embodiment, the invention includes a method of managing a power source with a two-tier approach. On a group level, the method includes retrieving cell data representative of the operating parameters of the cells of the group and managing the connection state of the group based on the retrieved cell data. On a system level, the method includes, retrieving group data representative of the operating parameters of the groups and managing the connection state of the group based on the retrieved group data.