Powering gadgets - battery banks or solar charger?

[sidpost]

I’ll give it some thought and hopefully I can field test it in the cloudy/raining uk weather this weekend

I got this one from Amazon for $26USD plus tax:

INIU Portable Charger, 22.5W 20000mAh USB C in & Out Power Bank Fast Charging, PD 3.0+QC 4.0 LED​

A little bulky overall but a really good unit at a modest cost from Amazon. It has a lot of functionality that isn't really needed so, a simpler one that is ~25% smaller may be worth it to you.