Patent ID: 7952326

Claim:
A battery pack configured to be interfaced with a hand held power tool, the battery pack comprising: a housing; a locking assembly operable to lock the battery pack to the power tool, the locking assembly including an actuator; at least three terminals including a positive terminal, a negative terminal, and a sense terminal; a plurality of cells, each cell having a voltage, power being transferable between the cells and the power tool, each cell having a lithium-based battery chemistry, the cells being electrically connected to one another in a partial parallel arrangement and a partial series arrangement; a battery identification resistor; and a thermistor indicative of a battery pack temperature; wherein a controller is operable to control a function of the battery pack, the controller being external to the cells and being operable with a voltage at least one of equal to and greater than an operating voltage threshold, the cells being operable to selectively supply voltage to the power tool as a function of the state of a switch and the thermistor; and the controller is operable to prevent the battery pack from entering an over-discharged state via the switch when the voltage supplied by the cells to the power tool is below a predetermined battery voltage threshold.