Hey everyone, I've been struggling through circuit design and with this forums help have been able to get almost everything in this project working... now I'm stuck on why my teensy isn't switching my p-Channel Switch( https://www.kynix.com/Blog/The-Best-Tutorial-for-P-Channel-MOSFET.htmlon/off.)

In case it wasn't already abundantly clear, electrical components are not something I have much (if any) knowledge about, so any and all advice would be greatly appreciated.

Here's my best attempt at a schematic;

Battery is a 12V Lithium Battery 51.2 Watt Hrs
Kasa smart switch AC50

Quick outline of the project;

1)There's a car battery that I pull 12V from and it is primarily used to charge the second battery.
2)That battery is hooked into the input of a DC Power Booster (charger) which has an external control cable (remote on/off).
a) When the charger external control switch is high the charger pulls from the car battery and charges the second battery.
3)The teensy reads the voltage on both batteries and is also sending data over CAN to a logging system.
4)When the teensy reads that the car battery is low it switches the P channel Mosfet off with a low signal
a)This MOSFET's drain is hooked to the External control so that when it is off the charger turns off.
5) When the teensy reads the second battery is low it turns off all the load components by cutting ground with an N channel MOSFET
6) When the teensy has switched both MOSFETS off it goes into a low power mode (Thank you Duff)


step 4 is where my problem is.
I've tried running source of the P MOSFET to both batteries. it doesn't turn on when hooked to the car battery, and doesn't turn off when hooked to the 12V battery.
At this point I'm 99% sure I just chose the wrong MOSFET or Transistor, but don't see where my error is or how to correct it.

Thanks in advance!