Banana Pi (m2 zero): cpu throttle on boot?

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 GUI).

The hangup occurs during services startup, usually around networking ones (quite often the last line is about starting OpenSSH server), so systemd is already on. And here's my question: can I throttle CPU during boot time, to curb down on power spikes and keep the current requirements without measureable limits, to prevent undervoltage? I know that there are no undervoltage-mitigating mechanisms in Armbian for Allwinner SoC's.

Also: what's the best way to measure momentary current consumption, with an oscilloscope? Via voltage drop on shunt resistor having 0.1 Ohm?

[1]