Intro To 18650 Li-ion Cells

Intro To 18650 Li-ion Cells

18650 is a size classification of lithium ion batteries. The name means that the battery is 18 millimeters wide, by 65 millimeters tall, and the zero means that it's a cylinder.

All cylindrical lithium ion batteries follow this same naming convention. Other common sizes are 16340, 14500, 17670, and 10440. 18650 cells are usually rated at either, 3.6, 3.65 or 3.7 volts.

For most cells, they're fully discharged at 2.5 volts and fully charged at 4.2 volts. Some 18650 cells can store over 4500 milliamp hours of power or provide up to 30 amps of current.

So that's nice and all, but who cares? How does this affect me?

Well first of all, you may not know this but you probably already own numerous 18650 cells. They're probably in the laptop battery that you're reading this blog post on. They're out in your garage inside your power tool batteries. And they're in your USB power bank that you use to recharge your phone when you're on the go. They're also used in some of the best and brightest flashlights on the market. There's probably hundreds of them in that electric vehicle down the street. And people who are really into vaping, use them to improve their vaporizer.

So why are these cells better than the more common double A batteries, or even C cell batteries?

For one thing, they have a much higher energy density, and higher load capabilities. That means they can provide more voltage and much higher current in a smaller form factor. They can also be discharged and recharged many more times and last longer on the shelf between uses because they have lower self-discharge. Finally, they can be charged very quickly with very simple charging algorithms.

I know what you're thinking. But are they safe? What are the drawbacks of these things?

All 18650 cells require a circuit to protect them whether they're a single stand alone battery or a battery pack. If it's a stand alone cell, they must have a built in circuit, or a button top, like a double A battery, which technically makes them 19670s or they require a battery management system if they are a pack.

A battery management system, or BMS, monitors the voltage of each individual cell in the pack, while it discharges and charges. But whether it's a button top or a BMS, it will prevent thermal runaway, which is what causes explosions and fires.

The other major drawback is that lithium ion batteries, in general, are getting harder to ship in large quantities without jumping through a bunch of regulatory hoops.

But despite these concerns, as long as they're not subject to really high temperatures, have a protection circuit, and they don't get abused, like being punctured, they're safe for common use.
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