A brief case sized battery pack for powering large power tools for use in portable applications. Large cordless power tools, such as torque guns, are often used to fasten very large nuts on wind turbines. AC power for charging may not be available depending on the location within the wind turbine. The portable rechargeable battery pack has several battery elements, each element able to power the cordless power tool. Using a selectable switch, a user manually selects the battery element to power the cordless power tool. The manually operable switch electrically connects to enable one of the first battery elements to be electrically coupled to the at least one DC output electrical connector while the DC output of a battery charger simultaneously charges all the battery elements. In one example, the DC output connector provides at least four positive DC leads all at different voltages plus ground.