I wanted to try using an external powerbank to overcome disposing of hundreds of AA batteries. I have tried a 5V powerbank supplied by RS (link at bottom of message). This is a reasonably compact size (101*66*16) and so far has powered an Audiomoth for multiple nights of recording without any power down/sleep problems. The only slight issue is some interference on the recordings, visible as faint lines every 500Hz (sample rate = 32kHz, medium gain).
I have tried three different USB cables and all show the same effect. I've confirmed this is not due to external soruces (lines are absent when using 3 AA batteries in same recording location).
This is probably bearable for my uses but does anyone know:
whether it is possible to overcome this;
whether its possible to be confident that these artefacts won't be any worse if I bulk buy more of the same powerbanks.