devices—and cylindrical cells that look like extra-large AA batteries and are used in rechargeable power tools and electric cars.[1] Lithium ion cells differ from common household batteries (e.g., AA, AAA, C and D) in three important ways. First, lithium ion cells are generally manufactured to accommodate the specific power demands of a particular device.[2] Each device may present its own unique power demands. Thus, a polymer cell from one model’s phone may not necessarily work in another model even if they are the same size. Second, lithium ion cells need to be handled carefully in order to avoid a thermal runaway event that could lead to a chemical fire.[3]
Third, for common household batteries, the size and shape of the battery—its form factor—indicates that it can be used in a device that accepts a battery of that particular size and shape. The common cylindrical version of a lithium ion cell, however, comes in a form factor called “18650” which refers to the cylinder’s dimensions—18mm in diameter x 65.0mm in length. Unlike the common household batteries, which come in different shapes and sizes, and are labeled by type, lithium ion batteries are the same size and shape (e.g. 18650 form factor) regardless of internal chemistry, and are not labeled by type or internal chemistry. As Kerchner of the PRBA explained at the Workshop while holding up two different 18650 cells:
So, for example, these two cells look exactly the same. They have the same dimensions. They’re 18650, 18 millimeters in diameter, 65 millimeters in length. This cell could have been designed to power a notebook. This cell could have been designed to power a power tool. If you mix these up, while they are the same size, and you put these batteries with these cells together, that’s where we’re concerned on some of the safety issues when consumers or repair facilities are unaware of the difference between these individual cells… And that’s important to recognize, that when you’re going in and you’re repairing products and you’re not aware of the differences between the different cell chemistries—and there are about six different lithium ion chemistries in the world today that are used, both for consumer and industrial products. There’s different chemistries. There are different designs to power certain products. And without that knowledge, there’s a lot of safety concerns that we, as an industry, have.[4]
As such, although they are the same size and shape, one 18650 cell may have a dramatically different internal chemistry from another. Yet an individual or independent repair shop may not be able to distinguish among 18650 cells because the cylinders’ labels do not
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