I’m a battery/small electronics geek.

Storing Li-ion at 100% long term is stressful to the chemistry. Better to store a 20k batt. at 50% than a 10k at 100% - penalty will be some additional cost/weight. Lots of good info HERE.

A 4xAA combo battery bank/charger would make sense loaded with LSD NiMh (Eneloops). NiMh can handle high current loads, although do not have the power to weight ratio of Li-ion. Eneloops also store very well long-term. Then in a pinch you could also use scavenged AA (or AAAs) alkaline batts (ubiquitous in every household) to charge USB devices, although the high current will kill alkalines fast. I personally use a pocket-sized 18650 battery bank/charger, and can use alkaline or NiMh too by linking three in series.

Personally, I like split 50:50 powerbank:solar set-ups. For 1lb a 10k powerbank (stored 50%) plus 10k (tested) solar panels, and for ~1/2lb I keep half that in my EDC/GHB bag.