Method and system for charging multi-cell lithium-based battery packs

A method of operating a battery charger, the battery charger including a housing, a controller, at least two terminals including a power terminal and a sense terminal to electrically connect to a power tool battery pack supported by the housing, the power tool battery pack including a plurality of lithium-based battery cells, each battery cell of the plurality of battery cells having an individual state of charge, the method comprising:

• supplying a charging current to the power tool battery pack through the power terminal;
• receiving, by the controller, an individual state of charge of at least one of the plurality of battery cells over the sense terminal;
• controlling, by the controller, the charging current being supplied to the power tool battery pack based at least in part on the individual state of charge of the at least one of the plurality of battery cells;
• controlling, by the controller, the charging current being supplied to the power tool battery pack by controlling the battery charger to supply the charging current in a plurality of pulses, the plurality of pulses each having a first period of time during which the charging current is being supplied to the power tool battery pack at a predefined amplitude, and a second period of time during which the supply of charging current is suspended, and
• controlling, by the controller, the charging current being supplied to the power tool battery pack by modifying the first period of time and controlling the second period of time to be constant.