For my project SamplerBox, I had done many extensive tests in the past and it was possible to successfully power a RPi 2 for multiple hours with such a small 2600mAh power bank (18650-battery inside), and even 7 hours with a better-quality battery (see my article here).
Of course, it was using a read-only filesystem for which a power failure was not a problem. (Along the multiple hundreds hours of usage, there was not a single SD card failure).
Question: I tried the same with a RPi 4 and it does not seem to work. I know that the RPi4 consumption is higher than RPi2, but is there a way to make it run on lower CPU speed / lower power requirement? More generally, is there a way to make a Rpi4 work with such common small power banks?
Note: I would like to avoid dedicated "powerbank RPi Hats" which are more expensive (and by the way, I already use the GPIO / Hat for something other else).
