My circuit works on battery or USB power. I want USB to be primary and 4xAA secondary source. When USB is present, batteries are not dichargged. Even batteries are not needed when USB power is present. Schema attached. I uderstand that voltage from USB close P-MOSFET (BSS84). When i plug USB, on mosfet source is voltage (without batteries). It gives about 23mA short to ground. This come from drain! I dont understand why. I measured mosfet with diode test. New mosfet gate to source 0V, on used mosfet gate to source 0,9V. I dont get why is this hapening. Voltages are far below maximum ratings in datasheet.