The powerbank capacity (capacity) is usually expressed in miliampere-hour (mAh) units, ie the output current that can be supplied in one hour. The duration depends on the given current. The 10,000 mAh powerbank can deliver 10,000 mAh of current for an hour, or 5,000 mAh for two hours.
Meanwhile, Wh is the unit that states the maximum energy output rating of a powerbank. Unit Wh makes it easy to compare the energy rating between different battery types.
To get this Wh unit, multiply the capacity number by the powerbank battery voltage (not the output of the USB port).
For example, the 10,000 mAh powerbank has a 3.85 Volt (V) battery voltage, then its energy rating is 38,500 mWh (miliwatt-hour) or 38.5 Wh.
Unit Wh is usually already stated in the written statement in the body powerbank. If not, then the user can calculate their own in the way above.
Capacity is directly proportional to the physical size of the powerbank. The greater the capacity, the greater the body of the powerbank.
Indeed there are a handful of manufacturers that offer large-capacity powerbank model, to reach the range of 26,800 mAh. However, this energy rating is still below the 100 mAh (96.48 Wh) for the category of "small batteries"