How does this circuit work, from the Sparkfun NRF91 board?
Why do you need two transistors?
https://i.imgur.com/5JCQNol.png
That’s actually a single component that has 2 MOSFET’s inside.
My guess is that just happened to be what we had on hand and went with it rather than keeping another part in inventory but there could be some other technical reason.
R3 and R8 form a voltage divider to scale VBAT to a voltage that the ADC can handle.
This divider will draw some current; in order to disconnect it from VBAT when not in use, they are using Q2B as a switch. R10 keeps Q2B off by default, and Q2A turns it on for measuring the battery voltage. Q2A and R10 ensure that the gate of Q2B goes high enough to fully turn it off.