The problem: I want to run my Banana Pi M2 Zero from a battery / powerbank setup. It works like a charm from a beefy powerbank capable of consistent 2A output [1], even with added 5" LCD screen to power at the same time and wireless keyboard transmitter.
BUT it does hang up hard, I guess due to undervoltage, when powered from a smaller, weaker powerbank with a single 18650 cell and max output of about 500mA (theoretically 1A but let's underestimate, I'll try to measure it with an oscilloscope).
Armbian with 4.19 kernel and Ubuntu 18.04 (but booting in text mode, without any GU