Reducing the voltage drop on a simple comparator driving a MOSFET to avoid LiIon overdischarge
This circuit won't really prevent draining the batteries. I suggest a solution involves 1 power PMOS, one NPN BJT, one Zener and a few resistors. Make the BJT conduct and pull the gate of the MOSFET low only when Vbatt >= Vz+Vbe.







simulate this circuit &ndash; Schematic created using CircuitLab

The Vz of TL431 can be tweaked using a pot.