Lithium-based battery pack

An electrical combination comprising:

• a power tool including power tool terminals;
• a battery pack configured to be interfaced with the power tool, the battery pack including
• a battery pack housing,
• at least three terminals including a positive terminal, a negative terminal, and a sense terminal, the at least three terminals configured to be interfaced with corresponding terminals of the power tool, and
• a plurality of rechargeable battery cells arranged within and supported by the housing, each of the battery cells having a respective state of charge, power being transferable between the battery cells and the power tool;
• a balancing circuit configured to detect a charge imbalance among the battery cells based on a plurality of voltages of the plurality of rechargeable battery cells detected at substantially the same time;
• and
• a control circuit configured to initiate a controlled discharging process to discharge at least one of the battery cells whose present state of charge is high relative to a present state of charge of another of the battery cells, the control circuit including a microprocessor.