Somewhere over the Pacific, about six hours in, the seatback screen dims and the phone that was supposed to hold your boarding pass, hotel confirmation, and translation app slides under 15 percent. That moment is the whole argument for carrying your own power. Aircraft USB ports are inconsistent at best, often capped around 5 watts, and on older cabin retrofits half of them simply do not respond. Treating the seat as a charging station is a gamble that gets less appealing the longer the flight.
The rules are the part most travelers get wrong, and they are not complicated once you see the logic. Lithium batteries go in the cabin, never in checked baggage, because a thermal event in the hold is far harder to deal with than one an attendant can reach. Capacity is measured in watt hours, not milliamp hours, so a 20,000 mAh pack at 3.7 volts works out to roughly 74 Wh. Most carriers allow up to 100 Wh without asking, 100 to 160 Wh with airline approval, and refuse anything above that. Since 2025, a growing number of Asian airlines have added a further layer: no charging the pack in flight, and no stowing it in the overhead bin. It has to stay where you can see it.
Box figures rarely survive contact with a discharge test, which is why testing writeups are more useful than spec sheets here. Korean coverage tends to be detailed on this particular category, partly because domestic cell manufacturing and a crowded retail scene give reviewers a reason to measure rather than repeat the packaging. A roundup like https://www.keeptopsecret.com/power-bank-recommend-2026/ shows the level of detail those comparisons run to, and the numbers that matter for flying, watt hours and PD wattage, read the same regardless of where you end up buying.
Narrowing that down to what survives a boarding gate leaves a short list:
- Printed watt hour rating on the casing, since a gate agent who cannot find it may refuse the item outright
- Capacity in the 10,000 to 20,000 mAh band, which stays comfortably under the 100 Wh line while covering two or three phone cycles
- USB-C Power Delivery at 30 W or higher if a laptop or tablet is in the bag
- Pass-through charging, so one wall outlet at a layover gate can feed the pack and a phone at once
- Certification marks such as UL, PSE, or KC, which airlines and hotels increasingly look for
- Weight under 400 grams, because a heavy pack is the thing you leave behind by the third trip
After that it is handling. Top the pack up the night before instead of hunting for an outlet at the gate, keep it in the seat pocket with the rating label facing out, and pack a short cable rather than the coiled one that ends up under the seat in front. None of it is complicated, and it turns the long middle leg into the part of the trip you stop thinking about.