If you watch the video it isn't quite what the headline suggests. The guy is collecting 18650 cells from old laptop batteries and using them with his own BMS to build a new battery. Not exactly mixing and matching rando used batteries.
Except that the dude is measuring every individual cell (remaining capacity, resistance, ...) and then builds his power packs from the good cells. Just look at his channel, he has lots of videos about the process and multiple thousand cells to choose from.
It's still mixing and matching. Different cells that have been used in different ways have different resistances. That causes each cell to charge and discharge at slightly different rates. Over time, you'll wind up overcharging one of those cells in relation to the others and burn your house down.
> most of these I have seen have the charge protection tabs on the top.
That depends on the cell.
Some cells have charge protection. Others don't. The 18650 cell is standardized only in size-and-shape. The actual protection, chemicals, and other specifications are completely different from cell to cell.
Heck, some 18650s have 3.2V nominal voltage, while others have 3.7V.
IIRC, charge protection causes a voltage drop. So some applications prefer to use unprotected cells (with the overall device implementing charge protection elsewhere). For example, Laptops probably have ONE charge-protection circuit somewhere in their construction, rather than 6-charge protection circuits (each cell). This simple fix will cause 1/6th the voltage drop compared to 6x individual charge protection circuits.
The amount of current a battery can deliver also varies. Flashlight forums where people sometimes want the maximum power output will point you to a couple of specific 18650 parts and a similarly small number of sources where you can be reasonably sure they aren't counterfeits.
(Some) manufacturers provide specs for their batteries, but most of them are coming from no-name factories in China with no reputation at stake, so there's either nothing published or it's exaggerated.
Just because something is in the shape of the 18650 doesn't mean that the chemicals inside of them are the same. Tesla's 18650s allegedly don't have Cobalt in them for example. Panasonic / Tesla have been working on "special chemical sauce" to make the cells work better for car purposes.
Even WITHIN a company, there are different specifications. Samsung's ICR18650-22F has different specs than Samsung's ICR18650-32A.
Lithium is a potent chemical that is EXPLOSIVE when mishandled. Lithium Fires cannot be put out by a class A, class B, or class C fire extinguisher. Lithium Fires CANNOT be put out by suffocation (they are self-sustaining and do not require oxygen). And sure, the cells are "Lithium-Ion" and not "pure lithium" (Li-Ion is a bit safer), but the potency of the core element here demands caution.
Energy storage works because you're storing energy. And if that energy decides to "stop being stored", you basically got a major, explosive fire on your hands.
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For hobby works (especially since I'm not in high-performance hobbies like Battlebots or RC Cars), I prefer the safety of NiMH cells. They're $2 each, sold by Duracell / Energizer / Panasonic / Eneloop.
The "failure" case of NiMH is that the battery vents a little bit of hydrogen gas (okay, also an explosive risk... but its not a lot of hydrogen). So basically, the cells destroy themselves if you abuse them, but otherwise vent relatively safely.
Furthermore, NiMH cells can be overcharged for days and remain fine. They're a lot more durable than Lithium Ion. In fact, a lot of NiMH chargers don't even have timers on them: a common technique with NiMH is to just keep them overcharging.
NiMH is heavier but otherwise nearly as energy dense as Lithium Ion.
Lithium Ion batteries do not contain any lithium metal. They are considered Class B fires. Do not use a Class D extinguisher on them. Water is an acceptable way to extinguish a Li-Ion battery. Most battery factories use water to extinguish Lithium Ion battery fires.
Lithium-METAL batteries on the other hand require a Class D extinguisher. They are not Lithium Ion batteries. They are single use devices and can NOT safely be recharged.
