Methods of charging battery packs for cordless power tool systems

In a method of charging a battery pack, the pack is inserted in a charger and an initial set of checks of cell voltage and pack temperature is performed. Once the initial set of checks is satisfied, the cells may be charged at a first constant current level. The first constant current level is adjusted to one or more lower levels of constant current until cell voltages of all the cells are within a full charge voltage window. The voltage window is defined between a minimum full charge cell voltage level and a maximum full charge cell voltage level. The charge may be terminated once all of the cells are within the full charge voltage window.