ZENDURE A6PD 20k mAh w/45w PD Powerbank

Definitely a good idea to have a powerbank (or three) on hand while traveling, especially abroad. Also, to answer your original question (I'm sure it's too late, but maybe helpful for posterity), the maximum powerbank size allowed in planes is 100 W-h, which generally works out to ~27000 mAh. Zendure also makes one closer to that size, but honestly, 20k mAh is plenty for most applications, and the form factor of this particular device makes it really easy to slide into a back pocket along with the phone it's charging, so I've had a great experience with it so far. Also, if anyone is wondering, yes, this model can charge up to a 2017 15" MacBook Pro via the USB-C port (charges at the full 45 W).