Thanks for the reviews Manuel.
I took a normal USB 1S3P LiPo pack and rewired to be a 3S1P pack. The USB A plug is wired like a balancing connector so with a simple adaptor cable I have a SOTA battery I can have in my carry-on luggage that is completely normal in appearance. Claimed to be 2.8Ah pack but probably nearer 2Ah TBH.