Just a quick question - anyone travelled with multiple power banks and how is this viewed?
According to legislation you may have a reasonable amount for personal use in carry on, but it doesn't state what a reasonable amount is.
I was thinking of taking a 20000mAh and 2x 10000mAh on an international flight. I'm not sure if this would be considered reasonable for personal use or not.
Note they're Xiaomi powerbanks, so they're sturdy casing with short circuit protection and an on button. This could mean they technically count as devices rather than spare batteries, but again, I have no clue.
It will depend on the countries you are flying to/through as well as the airline's country of origin. Most seem to allow 2x battery packs up to a combined total of 32000mAh, with single units not exceeding 2000mAh. I don't think any allow them to be placed in the hold baggage.
Some countries may be stricter, but I couldn't find any examples. I recently went through Thailand to Cambodia, and I'm sure on the Cambodia leg the mAh was lower, but I can't remember exactly.