The MAX1909 highly integrated control IC simplifies construction of accurate and efficient multichemistry battery chargers. The MAX1909 uses analog inputs to control charge current and voltage, and can be programmed by a host microcontroller (C) or hardwired. High efficiency is achieved through use of buck topology with synchronous rectification. The maximum current drawn from the AC adapter is programmable to avoid overloading the AC adapter when supplying the load and the battery charger simultaneously. The MAX1909 provides a digital output that indicates the presence of an AC adapter, and an analog output that monitors the current drawn from the AC adapter. Based on the presence or absence of the AC adapter, the MAX1909 automatically selects the appropriate source for supplying power to the system by controlling two external P-channel MOSFETs. Under system control, the MAX1909 allows the battery to undergo a relearning or conditioning cycle in which the battery is completely discharged through the system load and then recharged.