Consumers should not buy or use individual, loose 18650 lithium-ion battery cells without protection circuits due to possible fire risk, according to a warning just issued by the Consumer Product Safety Commission (CPSC). The commission says it is working with e-commerce sites like eBay to remove listings of loose 18650 cells, which are sometimes used in vapes, e-cigarettes, flashlights, and toys.

“[T]hese battery cells may have exposed metal positive and negative terminals that can short-circuit when they come into contact with metal objects, such as keys or loose change in a pocket,” the agency wrote Friday. “Once shorted, loose cells can overheat and experience thermal runaway, igniting the cell’s internal materials and forcibly expelling burning contents, resulting in fires, explosions, serious injuries and even death.”

Injuries related to exploding 18650 cells have been documented for a few years now, but the frequency seems to have increased along with their availability on sites like Amazon or from wholesale retailers.

One of the companies that makes 18650 cells, LG Chem, asked distributors of e-cigarette equipment in a late 2018 letter to stop selling them, warning that “[i]ndividual consumer use and handling” that could “lead to severe burns and disfigurement,” according to a report in The Atlantic. Samsung and Sony also warn consumers against using the cells.

When we first wrote this post, we had some questions why the CPSC seemed to be unilaterally warning against all loose 18650 batteries. “They are often misused as a stand-alone consumer battery, but do not have protection circuits,” writes the agency, but you can buy 18650 batteries that do come with protection circuits — see an example in the picture above.

But a CPSC spokesperson clarifies to The Verge that this ban doesn’t necessarily apply to every individual 18650 battery you might see sold online, only those that don’t have those protection circuits. This will hopefully mean fewer scavenged batteries from larger power packs (like the kind you’d in a Tesla, electric scooter, or power tool) get repackaged and sold online.

The 18650 isn’t the only Li-ion battery that has the potential for misuse, of course— you can buy standalone 14500 cells as well, which are roughly the same size as a standard AA but more than twice the voltage (don’t put them into your remote). You can also purchase the 16340, a rechargeable cell similar to the single-use CR123A you might put into a smoke detector. The CPSC isn’t commenting on why those aren’t included in the warning, but we suspect it’s because they’re less common and less dangerous.

18650 cells are larger, higher density, and often used in more heavy-duty commercial settings, and even power Tesla’s Model X and Model S vehicles — though the CPSC acknowledges that’s fine, since it’s their intended use. That said, there is a small but growing DIY community springing up around building custom battery packs for e-bikes and even electric cars using 18650 cells bought on the internet.

This isn’t the first time the CPSC has intervened in battery tech. Back when hoverboards were bursting into flames, the agency demanded manufactures recall their unsafe products and threatened to seize ones that were non-compliant at the border. The agency was also in charge of investigating when the Note 7 started catching on fire, although in that case Samsung worked with the agency to get the product recalled before the agency forced them to do so.

Update January 11th, 3:56PM ET: Added the CPSC’s clarification that the “loose” cells it’s worried about are the ones without protection circuits, not necessarily just a cell that’s sold individually.