By Nate Berkopec, TSAR IT Officer and OHV Team Leader. This article contains affiliate links. All proceeds go to Taos Search & Rescue.

I’m a computer programmer. I’m also a search and rescue team member with Taos Search & Rescue. Obviously, I like to combine my two hobbies: tech and SAR. SAR, as an “industry”, is actually usually quite technology-forward and eager to adopt new tech that might make us find subjects in the field faster. However, there’s just so much happening and so much tech available now that it can be easy to “miss” some of the new developments that might help make you or your SAR team more effective. One that I’d like to discuss today is lithium-ion batteries, and in particular, the “18650” battery format.

18650s are ridiculously more powerful than AAs

“18650s”, are they’re usually called, are a particular size of lithium-ion battery. They look like AAs on steroids, and that’s kind of what they are. A typical AA battery is about 50mm (2 inches) long, 14 mm (half an inch) in diameter, weighs 23 grams, and carries 2000 mAh of charge at 1.5 volts, or about 3 watt-hours of power. 18650 batteries are 65 millimeters long and 18 millimeters wide (hence 18650 – 18×65). 18650 batteries generally weigh about twice as much as a AA (~46 grams). They also have different electrical stats – most 18650 batteries carry 2500-3000 mAh of charge at 3.7 volts, or 9 to 10 watt-hours of power. So, while 18650 batteries are about 50% larger than an AA, they carry about three times as much electrical energy. Also, unlike AAs, they are rechargeable.

If all of these electrical terms are unfamiliar to you, here’s the simplest explanation I can give. Let’s compare electricity to water coming out of a garden hose. The water itself is electrical energy. Voltage is a bit like water pressure. A dribbling stream of water is like having low voltage, the same hose with your thumb over the opening is like increasing its voltage. Amperage is the diameter of the hose, and therefore the total volume of water (electricity) leaving the hose. Putting your thumb over the opening of the hose increases the voltage but decreases the amperage, because less water can come out of the hose at once.

AAs perform best at discharge currents of less than 0.5 amps. Trying to get more current from them (1 amp or more) can reduce their lifespan by almost 75%. As an example, if you tried to charge your phone with a single AA (most phone chargers operate at about 5 volts/1 amp), you’d probably need 4 AAs to get the job done in a little over an hour. A single 18650, which can maintain its full energy capacity even at discharge rates as high as 5 amps, can easily charge a phone in about 45 minutes and still have a bit of charge left over. Compared to our wimpy garden-hose AA batteries, 18650s are more like a fire hose: more volts (3.7 vs 1.5), and more amps (some 18650s can discharge up to 20 amps or more).

Besides being much more energy-dense than a AA battery, what else makes 18650s special? Well, first of all – they’re rechargeable. Alkaline batteries are one-use only – lithium-ions can be recharged for years. 18650 lithium-ion cells are widely used for rechargeable applications: they’re often used in laptop battery packs, and are even used in Tesla vehicles (they use thousands of them!). You almost certainly already have 18650 batteries inside your house inside of your rechargeable electronics. Many USB “power packs” you buy at the store are simply plastic containers around 18650 batteries. 18650s are becoming so common that even Wal-Mart has them on their store shelves now.

18650s have a variety of applications in SAR

That brings me to the first use of 18650 batteries in search and rescue: we can use 18650 batteries in USB “power banks” to recharge our devices in the field at high speed. I use a Thrunite C2 power bank for this purpose on SAR missions to recharge my iPhone, which I use as my primary GPS using the Gaia GPS application. Most regular “USB power banks” you can buy on Amazon probably use generic lithium-ion cells internally, but using one which allows you to load your own batteries, such as the Thrunite C2, is more convenient as it means that I can carry extra batteries for longer missions. Oh, and I can use the same battery type in my flashlight, too.

Flashlights: 18650s make brighter lights that last longer

Which brings to me the 18650 battery’s most interesting and powerful search and rescue application: flashlights.

Combining the high discharge current of an 18650 battery with advances in LED technology means that some absurdly bright flashlights have been developed in the last 5 years. Since many searches happen at night, this is obviously a great development for SAR.

Let’s talk about a popular SAR headlamp, the Black Diamond Spot.

The Black Diamond Spot uses three AAA batteries. (Sidenote: Many flashlight nerds really hate the 3xAAA configuration. They have lower power output and are difficult to change in the dark.) It weighs 88 grams with batteries, and emits a claimed 300 lumens. As for runtime, both Black Diamond and Petzl (another popular SAR/outdoor headlamp manufacturer) do not follow the ANSI FL1 standard when reporting runtime. This standard stops the test when emitted light is less than 10% of the light at the start of the test. Since Petzl and Black Diamond don’t use this standard, they run their lights until they go out completely and greatly inflate their runtime stats. What’s the point of a lamp that runs for “80 hours” when 95% of that time the headlamp is barely even visible?! Black Diamond claims a ridiculous 80 hours of light, however, given the capacity of 3 AAA batteries, runtime is probably closer to 8 hours at low settings, and 1 or 2 hours at high settings. And remember, about half of that runtime will be at less than 50% of the maximum stated brightness. The Black Diamond Spot (and most Petzl lights) is also not waterproof, though the manufacturer *claims* an IPX-8 rating. Unfortunately, this rating only applies for the LED itself and not the battery compartment, which leaks. A “waterproof” light which is only waterproof without any batteries in it is not a waterproof light. The Black Diamond Spot retails for about $30.

Compare this to a Wowtac A2S. The Wowtac retails for the same price, $30, and runs on one 18650 battery. On high settings, the Wowtac A2S emits a staggering 1000 lumens at a 120 minute runtime. The Wizard is actually waterproof (because the battery compartment is secured with a rubber o-ring), rated to 1 meter submersion (IPX7).

It’s kind of hard to put into words just how much more light is emitted by an 18650 headlamp than something like the Black Diamond Spot. On a recent search, I was using my Armytek Wizard Pro on its highest setting. When I turned my headlamp off, the other searchers remarked: “Wow, my headlamp isn’t really doing anything”. The difference is truly night and day. This brightness is extremely useful for locating clues. On my last search, I was able to pick out a fly fishing lure underneath a pile of leaves because the brightness of the light increased the reflection of the half-buried lure. It also helps to have a brighter light when man-tracking at night or even during the day. A bright light casts a strong, contrasting shadow over the ground and brings footprints into sharp relief.

At a brightness setting more comparable to the Black Diamond Spot, an 18650 headlamp will probably last 50-100% longer due to the increased energy capacity of the battery and superior discharge characteristics. The Wizard can also be easily detached from the headmount, which makes it useful when tracking footprints at night: one can detach the light from the mount, put it a few inches above the ground to increase relief and contrast on the track, then reattach to the head mount. Also, of course, it’s much easier and convenient to change one large battery in the dark than it is to change three small AAAs. My Wizard actually weighs half as much as a Black Diamond Spot (48g), so with a battery installed, probably weighs about the same.

Another common feature of many 18650-powered flashlights that I like – you can slightly unscrew the tailcap and “lock out” the flashlight, meaning that it will no longer turn on. This means you can safely carry these lights in your pack and not have to worry about them turning themselves on and draining their batteries.

18650s also make for extremely powerful handheld searching lights. I use an Acebeam T21, which uses 2 18650 batteries. On the highest setting, I can dimly illuminate a hill about half a mile away from my house. The Acebeam T21 costs about $150. It’s really hard to believe just how powerful an 18650 searchlight can be until you’ve seen one in person – they’re more like light cannons than flashlights. There are even more powerful models available which use 4 18650 batteries, and are about twice as bright and can illuminate another 500 meters further. However, I’m not sure how appropriate these would be for extended field use. Lights which use 4 18650 batteries are called “coke can” lights, because they are quite chunky and uncomfortable to hold.

Compare these light cannons to the light my SAR team currently uses as their “searchlight” – the E-Spot Litebox. The Litebox costs slightly more ($165), weighs 10 times as much (about 8 pounds), is half as bright (500 lumens), emits about ~1/8 as much light (55,000 candela), and has a battery which cannot be changed in the field. When running at a similar brightness level to the Litebox, my Acebeam T21 will last about 3 hours. The Litebox claims to last 7 hours. However, I can easily carry 2 extra 18650 batteries at about 50 grams each! The Litebox is “water resistant”, while the T21 is completely waterproof.

Hopefully I’ve convinced you that 18650 lights and batteries are the future. How do you get started?

First, you need a battery. Generally, a good 18650 battery should cost you about $6-7. “High capacity” batteries may cost about $10 each. I carry about 8 18650s into the field, but I’m also using 3 18650-compatible devices: a USB power bank, my Acebeam searchlight, and my Armytek headlamp. You can do the calculations for yourself based on manufacturer runtimes to determine how many batteries you need. Most 18650s have roughly similar performance, but unfortunately you do have to watch out for fakes. You’ll also want what’s called a “protected” battery. These batteries are slightly longer (a few mm) than regular 18650s due to the addition of a small circuit board on the battery. This circuit stops the battery from discharging at too high a current, which could cause a fire. You know how Samsung phones kept starting on fire on planes? Lithium-ion batteries do have that drawback. However, remember that 18650s are used safely every day in laptops and Tesla vehicles, and that most lithium ion cells don’t have any safety issues. If you’re only using 1 or 2 batteries in a quality light and your batteries have protection circuitry, you’ll be fine. Quality brands of 18650 batteries include Efest, Keeppower, Enerpower and Shockli. Don’t buy batteries on Amazon, there’s too many fakes. A trusted vendor of genuine 18650 batteries is illumn.com.

If you’re a cheapskate, you can even salvage 18650 batteries from old laptop batteries.

Second, you need a charger. These are cheap – $15-$20. Get one which takes different sizes of battery using a spring. Lithium ion batteries come in many different lengths and sizes. If you decide to use a different size of lithium ion battery in the future that isn’t an 18650, you won’t have to get a new charger! Here’s a good charger from Efest.

Finally, you need a light. This is the part where everyone has an opinion. If you’re interested in doing the research for yourself, you can check out /r/flashlight or Parametrek. If you just want me to tell you what light to buy, I can recommend the Armytek Wizard Pro ($85). A cheaper option would be the Wowtac A2S. As for searchlights, look for something that takes 2 18650s. As I mentioned before, it adds power without making the light too big to comfortably handle for long periods of time. I use an Acebeam T21. If you’re looking for a cheaper and smaller searchlight option, consider a Convoy C8s at just $25.

As for 18650-powered USB powerbanks, I’m really liking my Thrunite C2. It’s very small and fits anywhere in a radio chest harness. It’s also long enough to accept protected 18650 batteries.

I hope I’ve convinced you of the 18650 Gospel. If you’re a first responder and are using 18650 batteries in a way I didn’t cover, please email me and let me know what you’re doing!