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Cold Weather USB Charger

Cold Weather USB Charger

Written by Adam Press Mechanical Designer and CoFounder 

Winter is in full swing here in Canada, and when temperatures plummet, most people put away their camping gear until the spring. There are those among us however, who brave the cold temperatures in search of adventure, to test their endurance, or maybe because their job requires it!  If that’s the case, it’s time to invest in a cold weather USB charger.

Whether it’s a camera to get that perfect shot, or an electronic mug to warm up your drink, electronics can certainly add to your winter outdoors experience and our cold weather USB charger, WaterLily, can be perfect for these situations. Whatever your reason for heading into the unforgiving cold weather, if you plan to bring any kinds of electronics, we think you should know about the following topics:

Will I harm my USB device by using or charging it in the cold?

Lithium batteries found inside your electronics can be damaged by charging in temperatures below 0°C (32°F) so care must be taken when  using a cold weather USB charger to recharge your devices on cold days and nights. For example, Tesla cars are equipped with battery pack heater, to warm the battery before charging begins in cold climates. As well, when lithium-ion batteries are exposed to cold temperatures, their performance suffers. When cold, a phone battery can drain faster than normal, or it might say it has ample power remaining and then suddenly go dead. The problems are only temporary and the battery should behave normally when the device is brought back up to warmer temperatures. (1,2)

Battery University™ is a free educational website offering hands-on battery information to engineers, educators, media, students and battery users alike. They state the following about charging and discharging lithium batteries commonly found in battery banks, phones, and most high tech gear(3):

Charge Temperature Discharge Temperature
0°C to 45°C (32°F to 113°F)  –20°C to 60°C (–4°F to 140°F)

So while it’s ok to use your device across a broader range of temperatures, special care should be taken when charging.

“Although the pack appears to be charging normally, plating of metallic lithium can occur on the anode during a sub-freezing charge. This is permanent and cannot be removed with cycling. Batteries with lithium plating are more vulnerable to failure if exposed to vibration or other stressful conditions.”
Battery University™

Best practices for charging USB devices in the cold

So how can you avoid damaging your batteries when recharging in the cold? The best way is to keep your battery warmed while charging:

  • Run the charge cable right into your tent or shelter
  • Keep the device inside a pocket near your body
  • Wrap the device inside some insulating layers
  • Put the device in an insulated case or inside a blanket along with a chemical hand warmer or a rock that has been warmed by the fire or in a pot of heated water
  • Bring some low cost battery banks with you, and charge in two stages: inexpensive battery then expensive device.  So, in case damage does occur, it’s not your brand new phone or GPS that suffers.
  • Whenever possible, keep battery banks and phones IN your sleeping bag at night, and in an inner pocket of your clothing during the day.  

Does A Cold Weather USB Charger Actually Work?

We charged a battery bank outside overnight using WaterLily set up in a river, while the air temperature was -5°C (23°). We completely discharged the battery bank before starting the experiment. To keep the battery bank dry, we placed it in a ziplock back, and buried it in some snow.

The result?  In the morning we had harvested 6600mAH of energy. This was more than enough to charge our cell phones twice, and go-pro once. However, upon further examination back in our lab we found that this particular battery bank’s capacity had dropped as a result of this test. If we had followed the guidelines above for keeping the battery warm during the charging phase, this damage could have been minimized.

Does WaterLily work in sub zero temperatures?

The short answer is YES. Our lead electrical designer, Geoff Holden, has this to say about it:

“The WaterLily electronics have been engineered to perform equally well in cold and hot environments within a range of -20 to 60 degrees Celsius”
Geoff Holden
Lead Electrical Designer, Seaformatics

In fact, WaterLily’s magnets become stronger at low temperatures, and there’s less electrical resistance in the conductors. You can actually see an increase in power output making it the perfect cold weather USB charger! From a mechanical engineering point of view, keep in mind that like all plastic objects, Waterlily will become more brittle in extremely cold temperatures, so be mindful to avoid shock.

If you’re looking for more information on cold weather USB charging, or have any questions about using your WaterLily in cold weather, leave a comment below and we’d be happy to get in touch. In the meantime, check out some of the useful links listed below that we’ve referenced in this blog!

1) CNN – How to protect your phone in cold weather

2) Popular Mechanics – Does Cold Weather Injure Cell Phones?

3) Battery University – Charging at High and Low Temperatures


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