Thanks guys, so i've figured out I need a relay that the arduino can control, this will let me completely cut power going to the SIM800L and I can turn it back on when my RTC wake my Arduino.
I've had a look at your post Dannable and I have the exact same module (doesn’t have the voltage regulator built in). I was planning on using a buck converter (DC to DC), similar to the way you have 3, I only need 1.
The external batteries I’m looking at have 2 usb ports, that can both output 2 amps (per port) @ 5v, so i was going to run a usb from port 1, straight to the usb on the arduino and from port 2, splice the cables into a relay then from the relay into the buck converter that would be setup to output 4v (also need to make sure I get a buck converter that can output 2amps).
I'm not sure what and why you are using a level shifter though or where it sits in the circuit?
This also raises the question, should my battery be 12v instead of 5v if I’m using a buck converter? Will this also affect my choice of relays which most commonly and cheaply seem to be 12v?
Thanks,
-Anton