Energy: how 27000mAh might “become” 100Wh

Researching specs of charging banks, one might at first be confused by capacity comparisons.

The following is by my understanding.

I was reading about charging banks that might be used to charge a laptop. There seems a common limit of the capacity of those: airlines don’t allow more than 100Wh of energy storage without special permission.

Some places were saying 100Wh, while others, 27000mAh. In one place, it even said those are the same. Yet, from the point of view of physics, they can’t be, because a W (W) is not the same unit as a milliAmp (mA). Specifically, W measures power, while mA measures current. I knew more research was required.

It turns out it’s because many power banks use lithium-ion cells, which produce energy, internally, at around 3.7V.

So, since 1000mA=1A, and W=V*A, 27000mAh*3.7V=99.9Wh≈100Wh in the context of many power banks.

Source:

service.anker.com

benzo energy (Aug 20, 2019). “What type of cells is used for power bank?” https://www.benzoenergy.com/blog/post/type-of-cells-used-for-power-bank.html

“Guidelines for Batteries.” (Jun 10, 20206) Canadian Air Transport Security Authority. https://www.catsa-acsta.gc.ca/en/what-can-bring/guidelines-batteries

-js