Lithium Ion Battery Basics: What You Need to Know
If you haven’t shopped for an LED flashlight before, you might be surprised to learn that the brightest and most popular lights don’t run on AA, C or D cells like many of the lights from years past. Instead, most modern LED flashlights are powered by li-ion batteries. This li-ion flashlight battery buying guide will help get you up to speed on the current technology and explain everything you need to know to buy batteries for your flashlight.
Why li-ion batteries
As the popularity of battery-powered cars and electric scooters grow, more and more devices are harnessing the power of lithium ion batteries. LED flashlights are no exception. Simply put, li-ion batteries offer an energy density and performance that traditional AA, AAA, C and D cell batteries could never match. Li-ion batteries are also often rechargeable making them beneficial to the environment.
The end result? A battery that enables brighter outputs and longer runtimes from your flashlight while maintaining a slim, lightweight profile and adding the convenience of being rechargeable.
How li-ion batteries work
Lithium ion batteries work in much the same way as alkaline and ni-Mh batteries. An internal flow of lithium ions between an anode and cathode results in positive charge that is then distributed to your device when a circuit is completed. What sets these batteries apart is the energy density possible by the lithium chemistry inside.
If you’re interested in learning more about how li-ion batteries work, this guide from the Office of Energy Efficiency and Renewable Energy has an excellent layman’s explanation.
How to read li-ion battery names
How to read li-ion battery names
Li-ion batteries come in a range of sizes and capacities. Knowing what size li-ion battery you need is fairly easy once you learn how li-ion battery names are derived. Batteries usually are named with a 5 digit number that breaks down into the following:
The first two numbers represent the diameter of the battery in mm. So an 18650 battery is 18 mm in diameter and a 21700 battery is, you guessed it, 21 mm in diameter.
The next two numbers represent the battery length in millimeters. Going back to the 18650 example, the middle two numbers tell us the battery is 65 mm long and a 21700 battery is 70 mm long.
You might be wondering about the final “0” at the end of the battery name. This is because the final digit represents the shape of the battery and tells us it’s round!
By far the most common battery used by LED flashlights is the 18650. If you want to know more about 18650 batteries specifically and learn why this is the “gold standard” of flashlight batteries, check out our 18650 battery buying guide.
Li-ion Battery Specifications
Just like li-ion batteries can come in a variety of physical sizes, there is also a range of battery capacities available. A battery capacity, labeled in milliamp hours or mAh, clues us in to how much charge the battery can hold. What this means for you is the larger the capacity of the battery, the longer runtime you’ll get on a single charge.
Voltage lets you know the electric potential of the battery, or in simpler terms, how strong the electric current is when discharged from the battery. Most li-ion batteries have a low voltage between 3 and 3.7V.
Battery Output Current
While voltage tells us the strength of the battery output, we also need to know how much electrical current is flowing at a given time. For this we can look at a battery’s discharge rate which is measured in amps or A.
A standard, button-top 18650 battery will usually have a discharge rate around 5A (or often not list the discharge rate at all!). As advances in LED technology have demanded higher and higher outputs, nowadays you’ll see some flashlights like the EC23, MH23 and HC33 require a high discharge rate to enable the brightest modes. If this is the case for your flashlight, you’ll want to seek out batteries that meet the minimum discharge rate specified by the manufacturer.
Flat-top vs. Button-top
With a few exceptions, NITECORE flashlights require button-top batteries to function. Not only does this ensure a proper contact inside the flashlight, but the “button” is actually a small protective circuit that helps prevent short circuits and over discharging.
You might see some NITECORE batteries labeled as HP or USB-rechargeable and wonder what the difference is or when you might need these batteries. Here’s a quick run down of some speciality li-ion batteries available and when they come in handy.
Some flashlights need batteries with a high discharge rate in order to reach the brightest outputs. You’ll find batteries with an “HP” designation after the numerical name will provide high drain outputs that are often required to get your flashlight to reach the full brightness potential.
One good reason not to shy away from High Performance batteries: they’re backwards compatible! If you have an older LED flashlight that runs on regular old 18650s, you can still use HP batteries without worrying about the higher discharge rate affecting your device. We frequently recommend these batteries to anyone who currently owns an older model but thinks they might upgrade in the future to one of our high performance flashlights.
One of the newest advances in li-ion batteries is the introduction of USB rechargeable batteries. That’s right, these cells come with a micro-USB port built directly into the battery!
If you’re looking to minimize your carry or want to supplement a flashlight that doesn’t have a built-in charging port, these batteries are for you. Compatible with common USB power sources such as power banks, solar panels and laptops (and traditional chargers, too!), all you need to do is plug these batteries in to charge. An indicator light underneath the positive pole goes from red to green to indicate charging progress.
If you plan on using your flashlight in cold temperatures (think sub-zero), you might want to consider picking up batteries designated for use in low temperatures. Designated as LT in their model names, these batteries are optimized for, you guessed it, low temps.
Traditionally, CR123A batteries were the preferred power source for anything cold weather due to their chemistry’s superior performance. Now, NITECORE makes the NL1829LTP low temp battery, NL1829LTHP low temp, high performance battery and NL1829RLTP USB rechargeable, low temp, high performance battery — all designed to perform in cold temperatures all the way down to -40 F.