What are the various battery/cell types in power banks?

-The battery type use in power bank might be in different too from one to another. Due to the high manufacture cost for high-end Lithium-Polymer battery cell comparing it to Lithium-Ion, therefore, the price of power bank equipped with Lithium-Polymer battery is always rather higher than the power bank equipped with Lithium-Ion battery.

What is mAh?
mAh is short for milliAmp/hours. It's a measurement of the amount of energy the battery can store. The one with 8400mAh can store double the amount of energy that the one with 4200mAh can store.