Hot water is life — whether on a mundane level, as piping hot coffee keeps people sane and civilized during their everyday routines, or in a survival situation where the ability to sterilize water can keep you alive.

In RECOIL OFFGRID Issue 5, we reviewed a selection of insulated and non-insulated stainless steel water bottles. The best of the insulated bottles did a great job of keeping hot liquids hot and cold liquids cold. But all they can do is maintain temperature as long as possible. The Cauldryn Fyre water bottle takes that a step further by incorporating a heating element at the bottom of its stainless steel, vacuum insulated bottle. You can attach a large rechargeable battery to heat on the go, or dock the bottle on an AC- or DC-powered base and plug it into a wall outlet or cigarette lighter socket in your car or boat.

The One Bottle To Rule Them All?


With a name that Saruman would be proud of, the Cauldryn Fyre aims to do it all. The 16-ounce bottle is vacuum-insulated to maintain temperatures on its own. It’s topped with a screw-on lid with two openings — a small one that flips open to sip from and a larger spout with a threaded cap to pour from. The pour spout also sports a pressure release valve for boil mode. There’s a plastic clip strap that keeps the lid attached to the bottle and also includes a retention loop.

The heating element has two primary modes accessed via two buttons on the bottle: maintain and boil. The former maintains a specified temperature; you can cycle through four temperature ranges — 124-134 degrees, 135-145 degrees, 160-170 degrees, and 194-204 degrees. Initiate the boil mode and the element will stay on until the contents reach the boiling point (212 degrees). The four LEDs on the side of the bottle light up as the temperature reaches 104, 140, 176, and 212 degrees.

Keeping Hot Stuff Kinda Warm and Cold Stuff Kinda Cool

Unfortunately, as an insulated water bottle, the Cauldryn didn’t stack up well against the bottles we tested previously in Issue 5. To test the Cauldryn’s ability to keep its contents hot, we filled it to capacity with 200-degree water. After 12 hours at an ambient temperature in the high 60s, the water had cooled down to 80 degrees, a 120-degree difference. As a point of comparison, in our previous testing, the best-performing bottle from Zojirushi went from 195 degrees to 151 degrees after 12 hours, a loss of just 44 degrees, while the least effective of the products tested fell to 92 degrees, shedding 103 degrees.

For our cold water test, we filled the Cauldryn with 39-degree water. After just 15 hours, the water had warmed to and remained at ambient temperature, which was 65 degrees. In comparison, in our previous testing, the Zojirushi bottle again topped the charts, going from 36 degrees to 50 degrees after 24 hours, in an ambient temperature of 78 degrees. None of the previously tested bottles reached ambient temperature in the 24-hour testing period; the worst bottle crept up to 74 degrees after 24 hours.

Plan Ahead

So, the Cauldryn’s not a particularly good insulated bottle, having performed noticeably worse than the least effective product in our prior roundup. But it has something none of those other bottles have — a heating element. Using that element to maintain temperature turned out to be our favorite application for the Cauldryn, keeping coffee and tea at our preferred temperature all day without any fuss. We appreciated being able to choose between the different temperature options, even enjoying hot soup. The trade-off is that, due to its large battery, the Cauldryn has much lower capacity and weighs much more (a pound or more) than traditional insulated bottles. With the battery attached, it’s awkwardly tall, at over 12 inches.

We also tested the Cauldryn’s boil feature. Untethered, we were able to get two boils out of a fully charged battery. Starting with 16 ounces of 61-degree water, the Cauldryn delivered boiling water as promised, taking 18 minutes to reach 212 degrees with the lid closed. Without the lid, it took 20 minutes and reached 211 degrees before automatically shutting off. We thought this was a rather leisurely pace — until we conducted the next test.

The Cauldryn comes bundled with a handy AC-powered base on which you can dock the bottle. Perhaps our base unit was faulty, but it didn’t work well. Boiling 61-degree water with the Cauldryn plugged into a power outlet took a long time. The tree outside our office window seemed to be growing faster than the water temperature in the bottle. Perhaps taking mercy on us, the Cauldryn finally threw in the towel and shut itself off early at 199 degrees, after 51 torturously long minutes. CIA operatives take note: Waterboarding may no longer be an approved enhanced interrogation technique, but being forced to watch the Cauldryn boil water on its AC-powered base might be a close substitute.

Other Considerations


Boiling water takes a lot of energy, so the battery module is quite heavy (1.3 pounds) and boasts a robust 75.5 watt-hour rating. It’s also designed to recharge via a hefty 19-volt, 2-amp power supply. This is no big deal when you have access to AC power or use Cauldryn’s optional DC adapter. However, if you’re out in the field with the bottle and its battery, common portable charging options such as USB power banks or solar chargers won’t charge the battery, even with an (uncommon) USB cable that fits the battery’s thirsty circular plug.

Four LEDs on the battery display its status, and you can also charge other items with the Cauldryn’s battery via two USB ports. Both output 5 volts, with one rated at 1 amp and the other at 2.1 amps. While charging an iPad that regularly pulls up to 1.8 amps from a wall charger, we measured output up to 1.5 amps from the Cauldryn battery.

Some of the Cauldryn’s controls weren’t as user friendly as they could be. The maintain and boil buttons are unlabeled, so you need to remember which is which. The temperature LEDs are also unlabeled, but they’re color coded so it’s easy to get the drift. The 1A and 2A USB charging ports aren’t labeled either. You also need to mind the battery’s power button; we unintentionally actuated it several times. The retention loop arrived broken, but that’s OK because we didn’t like it anyway, as it’s made of plastic and protrudes inconveniently.


With exposed leads on the bottom of the bottle, you need to exercise some care in cleaning the bottle after use. You can’t just dunk it in the sink or throw it in the dishwasher.

There are many superior insulated bottles on the market that are also lighter, smaller, less expensive, and higher-capacity, so we’d suggest you only consider the Cauldryn if you plan to use its heating element frequently. We felt the sweet spot for the Cauldryn was in keeping liquids warm at your exact desired temperature — handy for everyday use or on short outings. However, if you don’t mind losing a little bit of temperature over time, a highly rated insulated bottle would be a cheaper, lighter, and more convenient option. The boiling function consumes so much battery power that we’d reserve it for emergency use when in the field — but it’s a nice capability to have and useful if you have ongoing access to an AC or DC power source. As a survival tool, though, the Cauldryn’s practicality comes up short.

Hot Water Test
2 Hours146°F
4 Hours121°F
8 Hours93°F
12 Hours80°F


Cold Water Test
 4 hours54°F
 8 hours60°F
 12 hours63°F
 15 hours65°F (ambient)

Make & Model
Cauldryn Fyre Mobile

8.25 x 37⁄16 (bottle)
4.25 x 3 3⁄16 (battery)
12 1⁄8 x 3 7⁄16 (attached)

1 lb. (bottle)
1.3 lb. (battery)
2.3 lb. (total)



STAY SAFE: Download a Free copy of the OFFGRID Outbreak Issue

In issue 12, Offgrid Magazine took a hard look at what you should be aware of in the event of a viral outbreak. We're now offering a free digital copy of the OffGrid Outbreak issue when you subscribe to the OffGrid email newsletter. Sign up and get your free digital copy

No Comments