A look inside a fairly common USB power bank sold on eBay. Note that I do not recommend that the output is loaded above 1A as demonstrated in the video, as 140C+ is way too high for semiconductor components!
Other than the slight undersizing of components for full 2A output, the unit is actually quite well made and fits a very large lithium cell into a rugged alloy case.
Jack Youngs pointed out that if the unit is using a buck converter during charging then the input mAh I measured is not going to reflect the cells mAh capacity, so it will actually be closer to 5Ah.
Here's a general search link for eBay.com.
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