Circuits designed to protect batteries in battery-powered equipment that also can be powered by another source, e.g. battery eliminators. The circuits have an ideal diode and automatically switch off the battery when another power source is connected. In active mode the voltage drop is only 28 mV and the reverse-current in switched-off mode is as low as 1 uA. The circuits handle input voltages from 2.6 to 5.5 V and currents up to 2.6 A.