The MAX1773/MAX1773A highly integrated ICs serve as the control logic for a system with multiple power sources. They directly drive external P-channel MOSFETs to select from an AC adapter and dual battery sources for charge and discharge. The selection is made based on the presence of the power sources and the state of the batteries. The MAX1773/MAX1773A detect low battery conditions using integrated analog comparators and check for the presence of a battery by using battery thermistor outputs. The MAX1773/MAX1773A are designed for use with a buck topology charger. They provide a simple and easily controlled solution to a difficult analog power control problem. The MAX1773/MAX1773A provide most of the power source monitoring and selection, freeing the system power management microprocessor (P) for other tasks. This not only simplifies development of the power management firmware for the P but also allows the P to enter standby, thereby reducing system power consumption.