Hey ReverseEMF, thank you so much!!
Please forgive my inaccurancy, I'm quite a newbie on this field.
The board I'm using is a NodeMCU Amica.
What I know so far is that its GPIO works ar 3.3v and the voltage drop between Vin and GND (when using the micro usb power source) is 5V.
I understand your concern about the high power consumption of the wifi chip, but in a realistic scenario the wifi chip will be on&connected for 15-20 seconds per day. I made a lot of work on the software side to keep its usage at minimum. In any other case, the wifi chip will be completely off.
If I understand what you wrote, I should use the dc-dc converter I already own (LM2596S) to handle the power coming from the battery.. but now, what type of battery do you suggest I use? Should I use 4 AA batteries?
I am not able to find the Nodemcu datasheet, so I am not sure what is the correct voltage to apply to Vin.
Thank you again for you help!
MJ