Authored by Jessie Cyr-
Let’s get this out of the way: I don’t know enough about the chemistry of these cells to speak to it, at all. I do know what happens when they are mistreated though, and for the purposes of nearly all users, that should be more than enough. 18650 cells are an extremely versatile platform. Being used in laptop battery packs, flashlights, power tools, and we as vapers have co-opted these high drain cells for our own purposes.
One thing to note here is that these aren’t just big “AA” batteries, these cells are meant for high amperage draw and high capacity. That makes them great for our purposes, but it also gives them the potential to be dangerous if mishandled. There are multiple failure states for these cells. The least dangerous failure state would be cell “venting”, which is to say a hole opens in the casing releasing pressure within the cell. This will ruin the battery, and likely make a mess for the end user to clean up inside their mod, but that’s preferable to the cell entering thermal runaway. In that case, the cell fails to vent safely and temperature within the casing increases until a catastrophic failure state is reached. When you see that grainy security camera footage of someone’s pocket catching fire, that’s thermal runaway.
How does this happen? It can be from a cell being left loose in a person’s pocket with keys or change, or it can be from the cell otherwise unintentionally completing a circuit with very low resistance and no protection circuit in place to prevent it from discharging above a safe amperage for that cell. Consider this, the entire cell is actually the negative terminal from the exposed base all the way up to the ridge around the positive post on top. If any conductive material happens to touch the positive post and any other metal surface on the cell, left unchecked this could cause the battery to reach one of the two aforementioned failure states.
Now that we know what can happen when we don’t take care of our batteries, why not talk about how to prevent that? It’s pretty simple for most users to minimize their risk with these cells. Before putting the cell(s) in your mod, take a good look at the battery wraps-- are there any nicks or cuts? What about the insulator near the positive end of the cell? Typically the insulator is a small white disk present around the positive battery terminal. Is this disk present? Is the cell itself in good condition without dents or other visible damage? What about the positive post? It should be standing flat at or slightly above the rest of the casing at the top of the cell.
If any of these circumstances point toward damage, do not use the cell until such a time as it can be repaired; replacement wraps are widely available, affordable, and replacement is a very easy process with a hair dryer or heat gun. It is a trivial matter to replace the insulator if it is damaged or missing. In the event of damage to the cell itself, it will need to be appropriately recycled; often this is as easy as speaking to an employee at a local vape shop or at an electronics retailer. If you’re carrying extra batteries, keep them in a case! Whether a silicone sleeve for each cell or a clamshell case designed to hold multiple cells, keeping the cells isolated from other metal objects is absolutely imperative to your safety when carrying extra cells.
All of this information is relevant for all users who have vaping devices with external batteries, regardless of the form factor or chemistry, but further precautions need to be heeded by users with mechanical mods. If a vaping device has no protection circuitry in place it is very important to understand the limitations of a given cell, and how that cell will behave with a given atomizer or build for a rebuildable atomizer. Having a solid grasp of Ohm’s law is an absolute necessity for using this type of device, trusting that the guy at your local shop, or one of your friends “knows what’s safe” without double checking the math and inspecting the coils is an incredibly risky proposition. In general at this point, mech mods certainly have their place for specific users, but for the vast majority of users it is preferable to operate with a regulated device for their own safety and for reliable performance.
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