The Xiaomi Power Bank - which works with any phone brand
From what they said, this power bank automatically gives the right amperage, It's impossible to give a phone all the 10,400 mAh you will fry it
By the way, the number you are fixating on here, is not what you seem to think it is.10400 mAh. means 10400 milli Amperes per hour.So it will be able to supply 10.4 Amps for an hour, or 5200 mA for 2 hours, and so on.Your Arduino will be running for hours and hours off of this power bank.
The Arduino can't handle Amperes, you'll have to switch range to milliamperes.