Battery Chargers for 18650 Batteries
There are two kinds of batteries: primary cells and secondary cells. Primary cells are like alkaline batteries, you use them once and throw them away. 18650 lithium batteries are secondary cells; you can recharge them so long as you have the appropriate charger. Most chargers offer two or four slots for different batteries and many can charge NiMH batteries as well as 18650 batteries. A good charger can ensure you have batteries ready to go no matter what you need it for.
What is a 18650 Battery?
A 18650 rechargeable battery looks a lot like a traditional AA or AAA battery from the outside, but it's very different inside. Each battery contains a single lithium-ion cell along with a printed circuit board to manage charging. This is one reason why they are often more expensive than smaller batteries.
- Size: Where a standard AA battery is 14 millimetres in diameter and 50 millimetres long, a 18650 battery is 18 millimetres in diameter and 65 millimetres long. It's enough of a difference that you can put both battery sizes in the same charger, but not usually in the same devices.
- Voltage: 18650 batteries offer a standard output of roughly 3.6 Volts as opposed to the 1.5 Volts of AA. Lithium Ion cells provide a nominal output of 4.2V that drops to approximately 2.5V as they discharge, so most batteries list the average voltage, which is usually between 3.6V and 3.7V.
How do You Charge a Lithium Ion Battery?
As secondary cells, lithium ion batteries need regular recharging; however, the battery chemistry of lithium ion batteries makes strict demands on how you recharge them. They take a strong current at first, then a saturation current to charge them the rest of the way. You can prolong the battery's life by not charging it all the way and then recharging before it fully discharges as this reduces stress on the battery. In some ways they charge similarly to lead acid batteries, but the following differences are important:
- Overvoltage: Lithium ion has no tolerance for overvoltage. An overvolted lithium ion battery overheats and can catch fire or even explode. Most batteries feature control circuits that cut off charging before anything can happen.
- Trickle Charge: You cannot leave a lithium ion battery on the charger continuously. Lead acid batteries need a constant charge to stay topped up, but lithium batteries need to discharge and then recharge rather than ride a constant current.
Choosing a 18650 Battery Charger
When choosing a battery charger for your 18650 batteries there are a few things to consider. Your 18650 charger needs a cut-off to prevent overvoltage. Vapers may prefer a four-channel model to a two-channel so they can charge more batteries when hosting groups. You may also consider a 18650 USB charger for the flexibility it offers, as USB is everywhere.