The MAX1666 provides complete protection against overvoltage, undervoltage, overcharge current, overdischarge current, and cell mismatch for 2-cell to 4-cell Lithium-Ion battery packs. The voltage of each cell in the battery pack is checked and compared to the programmable threshold and to the other cells in the pack. The MAX1666 protects the battery pack in an overcurrent condition by disconnecting the pack from the load at a programmable limit. On-chip power MOSFET drivers control external P-channel MOSFETs to disconnect the cells from external terminals when faults occur. The MAX1666 employs a unique timing scheme that allows three modes of operation, for optimal performance and battery power conservation. The MAX1666 can operate in a stand-alone configuration or in conjunction with a microcontroller. It is available in three versions: the "S" version monitors two Li-Ion cells, the "V" version monitors three cells, and the "X" version monitors four cells.