Building Your Own Arduino
From https://arduino.stackexchange.com/questions/35619/how-much-current-does-an-arduino-mega-draw-from-a-lipo-battery-5-000-mah - have these links:
What you can do is build your own 'less greedy' Arduino and use sleep abilities of AtMega chips.
Here are some links to go through:
https://openhomeautomation.net/arduino-battery/
https://circuits.io/circuits/1717500-power-rail-blocking-with-an-arduino/
