# Design confusion with a MOSFET as switch

I am trying to design a simple battery operated circuit (ESP8266) controlled by a MOSFET (schematic below).

I was going through some videos to understand better and came across this video.

He talks about about the MOSFET VDS requirement to be 0.5 V at 2.57 time. He is subtracting the min voltage requirement of ESP8266 which is 2.5 V from a battery voltage of 3.0 V and thereby determining the VDS to be 0.5 V.

I thought the VDS is the max voltage that can flow between the source and drain terminals which in this case is 4.2 V. What am I missing? Are the following calculations correct? I seem to be confused with this.

The P-channel controls the high side positive rail to MCU while the N-channel controls the P-channel MOSFET.

VDS(max) across PFET will be maximum 4.2 V and min of 3 V when used with a LIPO.

VGS(min) across PFET = -3 V

VDS(max) across NFET will also be 4.2 V

VGS(min) across NFET = 3 V

IDD continuous across PFET will be a max of 300 mA