Abstract: A battery pack comprises a housing and a module holder. The module holder includes a plurality of core pack modules. Each module may have five sets of battery cells. The five sets of battery cells may be connected in series to each other. The core pack modules of the plurality of core pack modules are connected in series with each other.

Abstract: A power tool system that includes a power tool having a receptacle for receiving a battery pack, the receptacle including a mechanical interface for mating with a battery pack, a first battery pack having a battery pack housing, the first battery pack housing including a mechanical interface for mating with the power tool, the first battery pack housing having a first width dimension in a direction generally perpendicular to a direction in which the first battery pack mates with the power tool and a second battery pack having a battery pack housing, the second battery pack housing including a mechanical interface for mating with the power tool, the second battery pack housing having a second width dimension in a direction generally perpendicular to a direction in which the second battery pack mates with the power tool, wherein the second width dimension being at least about 1.5 times the first width dimension.