I have a few esp32 WROOMs and have finished building a water tank level monitor using a HC-SR04 sensor. I was hoping I can get the esp to go into deep sleep and have the batteries last for months (years) but it appears the wroom board is terrible at low power. So now I'm thinking to use a very low power micro (Arduino pro mini?) to switch the esp32 circuit on and off.
Does this make sense? Would I use a transistor or a mosfet?
Many thanks
A MOSFET is a transistor! 
You could use either.
Or does the ESP32 have some sort of a "shutdown" input that you could use?
Take a look at the TPL5110 and TPL5111 power switches/timers.
Wow that's perfect thank you!!
Sorry I'm mostly software wired xD It can shut down, but then won't wake up. In lower power timer mode it uses 20 mA which is huge. The DFrobot FireBeetle is much better but I still have to deal with the sonar using power. The TPL5111 seems the way to go.
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