A single 18650 cell is often used as the rechargeable battery for flashlights and e-cigarettes.
When combined together to create a multi-cell battery, 18650 cells are used for:
- power tools
- electric vehicles
- notebook computers (though today many notebooks use lithium polymer cells instead, which allow for a thinner form factor)
18650 cells are available as either "unprotected" or "protected" cells. The protected cells have a built-in circuit within the cell package that protects against potentially dangerous situations like over charges, over discharges, and short circuits - any of which can potentially lead the cell to burst, overheat, or catch fire.
Potential confusion with incompatible chemistry
The 18650 cell standard only specifies the form factor; the internal chemistry of the cell (and its performance and safety characteristics) can may dramatically from model to model. Concerns about this for 18650 cells in particular have been raised by right to repair advocates. A 2021 US Federal Trade Commission Report states:
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 contain information pertaining to the cells' internal chemistries or the products for which they were designed. The use of 18650 cells with the same form factor but different internal chemistries creates the risk that a replacement 18650 will have a different internal chemistry from the original 18650, placing individuals and independent repair shops at risk of inadvertently causing thermal runaway events.
Although the 18650 cell is a standard size (the dimensions in millimeters are in the name itself), cells with integrated protection circuits are often longer than the standard 65mm. Such protected cells usually fit in holders that use spring-loaded or flexible metal contacts, but other holder designs or battery pack formats may not fit them if they are designed for the standard 65mm length.