Are battery packs allowed in hand luggage?

I've had two battery packs / power banks, and travelled to several countries with several airlines, taking them as carry on, without any problem...until...

Last year, I flew from Tokyo Haneda, via Beijing, China to Vancouver, Canada. In Beijing, Chinese officials sent me to a security point, where several people including myself had our power banks taken off us, to our protest. More on the situation here.

In the end, I believe - from what they told me, it was because it didn't indicate the amperage / capacity anywhere on the device. Which seems pretty dumb to me for a reason - it's still a commercially made product (made in CHINA), but yeah, they confiscated it.

I also saw signs in Taiwan stating that they had to be in carry-on, NOT checked luggage for some flights, so yeah, you should be fine taking it in carry-on.

There have been rules re carrying batteries for many years.
They may be found in (at least) IATA documentation and also a number of courier companies and most battery manufacturers have advice documents.

Removable batteries must be carried in carry-on luggage with the exception mentioned below. Having batteries in carry=on makes sense - would you rather have a fire in a cargo hold or an overhead locker. (Answer: No! :-)).

There is an upper limit to the amount of Lithium metal that may be carried. Some manufacturers provide specific mass of Li per battery. Otherwise they have a linear conversion between Watt hour of battery (Vbat x mAh.) and Li metal.

On one occasion I travelled with a laptop with large battery, + spare battery + 2nd laptop + maybe 6 x camera batteries (7V2 x ~= 1500 mah). I was approaching but still under the Lithium metal limit.

China are a power unto themselves - they make up rules that others do not have. Export rules for batteries via eg Fedex do not apply to hina battery exports. Batches of batteries need a per batch test house certification that they meet certain standards. This apparently excessive zeal is because people are willing to ship dangerous junk and misdeclare it. Presumably the certified test houses have had it made very clear what will happen if they pass junk.

There are rules re battery carrying which vary somewhat. Some systems allow carrying loose batteries with ends taped otherwise rendered"safe" from accidental shorting. .

Sealed lead acid batteries that are spill proof(and not all are!) must be carried in checked luggage with a formal label stating that they are exempt under IATA regulation xxx. This actually works. I have seen signs that luggage has been opened and the battery checked but not removed.

Assuming that your 10500 mA?hr battery pack operates at 3.7 V, the energy capacity would be 3.8 V × 10500 mA?hr ? 40 W?hr. (Lithium-ion cells typically operate between 3.2 V and 3.8 V.)

By IATA guidelines, that would be well under the 100 W?hr limit for lithium ion batteries. The IATA guidelines list additional conditions to be met as well. (They must be genuine, certified batteries, for personal use, in reasonable quantities. If being carried as spares, they must be protected from short-circuiting.)

Mine with 20000 maH was taken by the officer in charge at Krabi's Airport. According to them it is too big and they can't allowed me to carry it.

Answer A: It will depend on the capacity in Wh (watt hours) but most commercially available ones should be OK. The IATA guidelines say that under 100Wh (multiply Ah x V to get Wh) is OK to bring on board and in cargo if installed in equipment. If they are loose spare batteries you can bring as many in carry on but not in the hold. Between 100-160Wh same applies but you are restricted to 2 spare loose batteries and again not allowed to check in. If over 160Wh you have to declare it and it has to be packed in cargo under the Dangerous Goods guidelines.Most airlines follow the IATA guidelines.

Answer B: only restriction I found was that the battery must be under 100Wh. Keep in mind that you have to validate the rules for any Airlines you will be flying and the airport rules if they are not in the US. It must be in hand luggage and not in a suitcase in the hold.

Answer C: They may be found in (at least) IATA documentation and also a number of courier companies and most battery manufacturers have advice documents. Removable batteries must be carried in carry-on luggage with the exception mentioned below. Having batteries in carry=on makes sense - would you rather have a fire in a cargo hold or an overhead locker. There is an upper limit to the amount of Lithium metal that may be carried. Some manufacturers provide specific mass of Li per battery. Otherwise they have a linear conversion between Watt hour of battery (Vbat x mAh.) and Li metal.

Answer D: It's fine in your carry on-luggage only. Batteries are not allowed in check-in luggage, only in carry on-luggage where they can be monitored. Here are the rules for batteries:

In order to ensure air transport safety, FAA,IATA, Airport has issued relevant regulations to regulate air passengers and crew members carrying power banks on to flights. The rated energy of power banks which can be carried on board is restricted and identification method for rated power has also been specified. For details, see the “Announcement of Rules for Air Passengers Carrying Power Bank onto Flights”.

More at: https://powerbankfans.quora.com/When-flying-are-you-allowed-to-bring-external-battery-packs-power-banks