I mention 18650 batteries so often in my headlamp and flashlight reviews, that I thought I’d do a dedicated article on 18650 batteries. 18650 batteries are rechargeable lithium ion cells used in laptop power packs, Tesla cars, high powered vapes, electric bikes, heated jackets, high power laser pointers, flashlights, headlamps, and many other battery applications. Realistically, all 18650 batteries are made by a select few number of companies including Panasonic, Sanyo, Sony, Samsung, and LG.
Chinese 18650 Batteries
eBay is chock full of 18650 batteries from China bearing names like “Ultrafire”, “Skywolfeye”, “Trustfire”, and the like. Most of these are batteries that started life out as something else entirely and were reconditioned and/or re-wrapped with a different label. Sometimes, they’re tired batteries from old laptop power packs, sometimes they’re different cells. In general, buy name brand (Panasonic/Sanyo/Sony/Samsung/LG) batteries from stores you can trust.
What Size are 18650 Batteries?
Technically, 18650 batteries are 18 x 65mm. (0.71 x 2.55″) The 18×65.0 mm is where the “18650” name is from. In terms of size, they’re taller and thicker than AA batteries, but not as thick as C batteries. Width wise, they’re similar to CR2 batteries that we used to use for old timey film cameras. In fact, most flashlights and headlamps that use 18650s will also accept 2 stacked CR2 batteries.
Are 18650 Batteries Dangerous?
Well, kind of. If the cells are physically damaged, overcharged, or undercharged, they could light on fire in what’s called a “thermal runaway”. 18650 batteries are different than lithium polymer batteries that you’d find in a cell phone in that they have a rigid outside casing that helps them withstand damage. Lithium ion batteries are therefore a bit more resistant to physical damage.
18650 Battery Capacity
Since they’re all running at 3.7 volts, there’s not much difference there, the difference is instead in the capacity or lifetime of the battery. This is usually expressed in mAh (milliamp hours) and they’re usually around 3000-3600 mAh. When you see a preposterous capacity of “5800 mAh” on a battery, it’s safe to assume that it’s a counterfeit and that real capacity could be anywhere from 400 mAh to 2000 if you’re really lucky. Poor quality batteries will also have undesirable internal impedance or resistance.
18650 Battery Drain
18650’s offer a relatively good level of discharge when needed but sometimes, it’s not enough. To support high power use cases, you need a “high drain” battery. These batteries don’t always offer the highest capacity and lifetime, but can provide more current and peak power. Some of these batteries will support 20+ amps of drain. For example, the Sony US18650-VTC5A can handle up to 35 amps of discharge as long as it’s kept under 80 degrees Celsius. If you’re looking for batteries for a high discharge device like a high power vape, look for max continuous discharge specs.
For most consumers out there looking for a battery for their new vape, flashlight, or laser pointer, the answer for “which 18650 battery should I buy?” is easy: something name brand from an in-country source. Chinese batteries are for messing around with; you won’t get the same lasting power and they aren’t as safe as name brand batteries. If you’re looking for the best capacity, get the Panasonic NCR18650G at 3600 mAH. But keep in mind that there are plenty of perfectly serviceable 3000-3400 mAh batteries out there that are cheaper, more readily available and are almost as good on capacity.