Is your office cold? These power banks double as hard warmers - on purpose

ZDNET's key takeaways

The Zippo Heatbank 6 and Heatbank 9s Plus are reasonably priced They warm up fast, but stay at a safe temperature They have a long runtime.

One of the tests I subject power banks to is a thermal stress test. I charge and discharge as aggressively as possible, both with and without a blanket insulating them. This simulates the power bank being carried in a pocket or bag -- and I closely monitor the temperature they reach.

If they get too hot, they are eliminated. My right eyebrow starts to rise at about 45°C/113°F, despite the fact that according to ASTM C1055 (the Standard Guide for Heated System Surface Conditions that Produce Contact Burn Injuries), the average person can touch objects up to 60°C/140°F for up to five seconds without sustaining irreversible burn injuries.

But, this winter, I've been testing power banks that are designed to get hot because they double as hand warmers.

Yes, you read that right, hand-warming power banks.

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Before I go any further, let me tell you a secret. Over the past few months, I've tested over two dozen hand warmer power banks, and none had what it took for me to publish a review on them. Some were dead on arrival, had an absurdly short runtime, or got hazardously hot.

But I finally found two power banks that made the cut, both from a company with a track record of making fire, flames, and heat.

Zippo, a company better known for its flick-top lighters, has a couple of hand-warming power banks: Heatbank 6 and Heatbank 9s Plus. 

Tech specs

Both power banks are small, candy bar-sized units with a very minimalist user interface -- both have a button for switching the unit off and on, a microUSB port for charging, a USB-A port for power output, and a basic interface for showing if it's on, the battery level, and the heat level (the Heatbank 9s Plus has a tiny LCD, while the Heatbank 6 uses a series of small LED lights). The Heatbank 9s Plus also has an LED flashlight feature.

There are slight spec differences, with the Heatbank 9s Plus having a 5,200 mAh battery and six heat settings (three settings and the ability to heat one side or both), while the smaller Heatbank 6 has a smaller 4,400 mAh battery and three heat settings (the whole power bank heats up).

And they work really well. The heat ranges from subtle to obvious, but never gets to the point of feeling overpowering or intense. For the best battery longevity, I'd recommend starting at the lowest setting and working up, because just a little bit of heat is enough to take off a chill sometimes.

And if you want to warm your core, add the neck lanyard and wear it beneath your coat. It's a good way to really warm up on a cold day.

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As a power bank, both Heatbanks are a little underwhelming. I consider USB-A output more for legacy devices, even though you can charge the latest and best devices with the right cable. Recharging the power bank using the microUSB port means it takes well over an hour to charge the smaller of the Heatbanks.

But remember, this is a hand warmer first and a power bank second. There are far better power banks on the market, but I've yet to come across a better hand warmer.

One word of note -- it is rather disconcerting to have a power bank that heats up! I've had a few "ooooh… that feels wrong" moments, and the fact that the Heatbank 6 looks so much like a regular power bank.

But after extensive testing -- and the fact that the product has been independently tested by UL Solutions -- I'm confident in the safety of these hand warmers.

ZDNET's buying advice

Both the Zippo Heatbank 6 and Heatbank 9s Plus are reasonably priced, with the Heatbank 6 at around the $35 mark and the larger Heatbank 9s Plus about $60. Given a choice, I'd go for the bigger, more versatile Heatbank 9s, primarily because I like the fact you can choose to warm one side, and on low, that gives a good day's runtime. That said, both are great and come in a variety of colors to suit.