Brrrr... It's Cold Out There! Managing Lithium-Ion Style Batteries in the Cold
OK, so it's cold this New Year's Eve, really cold for some of you in the country. The photo at the left shows the expected temperatures this New Year's Eve. Don't be getting frostbite! One of the concerns for pyros operating in cold weather is "Will my batteries be OK in the cold?"
In short, yes, but with some considerations. No battery likes the cold, since they create electricity through chemical reactions, and chemical reactions tend to go slower the colder it is. Mongoose and some other firing systems use forms of Lithium Ion batteries. Mongoose uses Lithium-Iron-Phosphate (LiFePO4) chemistry, which behaves somewhat better in the cold than Lithium-Polymer (LiPo) batteries, but they are close enough in behavior to treat the same for this article.
When it is very cold (0 degrees Fahrenheit or lower), the internal resistance of the battery goes up significantly. What this means practically, is that while the battery still functions, it is far less efficient, wasting a lot of it's energy overcoming the internal resistance. The internal resistance is temperature dependent. So while the Mongoose electronic components are rated to -40 degrees Celsius (which oddly enough also -40 degrees Fahrenheit), the batteries need some thought when operating in really cold conditions.
There are really two options for maximizing battery performance in really cold weather (less than 10 degrees Fahrenheit):
Assume they will need to be on for a shorter time
Find a way to keep them somewhat warmer (above 20 degrees F would be best)
I don't recommend using the Mongoose units without some warming aids in conditions that are less than -10 degrees Fahrenheit, but if it is warmer than that, they will tolerate the temperature, but you need to assume that the normal 17+ hour running time on a charge might be reduced to as low as a couple of hours because of the greater internal resistance. So if you power it up, test continuity, power it down, and then power it up again shortly before your show, things should be fine.
Some people think that if there is a large internal resistance the battery should "self heat" once it is powered on. While some self heating does occur, it it too little to overcome the environmental cooling in most cases.
If you are operating even colder, or just want to warm things up to give yourself more breathing room on the available operating time, there are three things you should consider.
Keep the units in a warm environment (passenger compartment of truck versus trunk) until they need to be attached.
Put some insulation around the unit
Add heat (usually in the form of "hot hands" foot warmers).
Personally I like hand/foot warmers and bubble wrap. First give some foot warmers a good activation by blowing through the package. Foot warmers usually give off more heat than hand warmers. Blowing through the paper package after removing it from the airtight store package adds moist air to the mix, which causes them to become warmer than with dry air (since they rely on a rusting/corroding process when exposed to air to generate heat). They take about 15 minutes to generate the most heat, and mist last for 45 minutes to an hour, so plan accordingly.
Then tape a few of these to the underside of the Mongoose field unit (where the battery is mounted). Some people have even opened the unit an tapes packs to the top of the battery itself. Either works. Just remember to take the hot packs out after use if you put them inside.
Then wrap the whole thing in bubble wrap, working around the antenna and cables. Some people put it in a Styrofoam cooler (which acts as a warmer in this case), and isn't nearly as flammable at -10F. Others like to build "envelopes" out of bubble wrap and slide the units in. Here's a picture from one user that used metalized bubble wrap.
Insulating and warming can help any type of system that runs on batteries, as all batteries chemistries work less efficiently in really cold weather. Mongoose was designed with large capacity batteries specifically to overcome cold as well as give long life in the summer. It was designed for being able to shoot New Year's Eve shows in the mountains of Colorado. Unfortunately, this year it looks like most of the country will feel like the mountains of Colorado!
Have a great New Year's Eve and a Happy 2018 from all of us here at SimpliFire! Stay Green and Stay Warm!