I have several lithium batteries in my garage that go with yard maintenance tools. I usually bring them into the house for the winter, but lately I’ve been reading reports of batteries exploding and causing fires.
I’ve tried looking online for guidance but I’m running into conflicting pieces of advice. Many sites say that cold weather charging takes longer and batteries won’t hold a charge as efficiently when cold, but there is no indication as to whether the cold causes any damage or shortens the life of a battery.
So, assuming you live in a northern climate, what do you do with your outdoor batteries when it gets very cold outside?
Cold temperatures won’t immediately destroy lithium ion (Li-ion) and lithium polymer (Li-Po) batteries but sudden changes or gradients in temperature can do mechanical damage that mechanically damage the substrate, substantially degrading performance or even making the battery more prone to overheating or fire. The general guidance is to not heavily load batteries that are at a sub-0 °C temperature until they warm up through internal heating, or else use battery packs with internal heating elements, and allow the elements to first warm the battery before use. I would recommend discharging them to half capacity (which will significantly reduce the likelihood of spontaneous combustion) and storing them in your house or temperature controlled storage to maximize life and health of the battery. Lithium phosphate iron (LiFePo4) are very unlikely to spontaneous combust, and you can store those inside even fully charged without concern (though for long duration storage you should still discharge them down to about 50% for best life).
Cold batteries will show dramatically less performance and will be reduced in total energy-cycle life just because chemical reactions are less energetic at cold temperatures. There is some work being done on electrolytes to improve performance and cycle life operating at cold temperatures but for batteries that are typically used above freezing, just storing them in reasonably controlled conditions and making sure they are above 0 °C before loading should be sufficient for conventional lithium batteries.
Echoing @Stranger_On_A_Train’s comments, yes, I try to bring in my garage batteries and store them at about half charge for the winter. Generally, after my last bit of yard work, I’ll skip charging the batteries, and just put them in the basement.
It’s my understanding that it’s a bad idea to let lithium batteries freeze, but that the cold will slow down degradation. For this reason I often store small batteries that won’t be used for a long time in the refrigerator. For example, I have heated ski boots, and in the summer the batteries live in the refrigerator.
IIRC some instructions I had, the batteries will not charge below freezing. I had a solar-power-charged security camera which was esssentially useless for several months of the year, unless I brought the battery in and charged in indoors. The same applies with my tesla, until the car has been going a while and the battery warms a bit, in subzero temperatures, it cannot do regenrative braking. (The Tesla charger process will warm the battery if necessary)
I’m not concerned about the batteries charging or being useful in the cold - I won’t need them in the winter. In my case I’m talking about lawn care tool batteries.
My main question is bring them indoors (fire risk?) vs. leaving them in the garage, where the temp could approach 0 degrees F.
I’m slightly phobic about Li-ion batteries myself, as there are regular news bits about batteries catching fire. To be fair, quite a number of them were cheaply-made scooters, hoverboards, or vape pens, but there have been some cases of cars (from which one expects better quality) catching fire:
and even Boeing nearly lost a few planes due to battery fires:
Heck, my first phone (a Samsung Galaxy S6, but note a Note) almost caught fire several years ago. It got extremely hot and the battery swelled, bending the display (this actually happened during a flight). After I got home, I left it on and placed it by itself on the concrete floor in my garage until the battery went flat, and never used it again.
The best advice is to follow the instructions in the owner manual for your battery. For my lawn equipment batteries, that means storing them at ~50% charge. I think the fire risk is pretty low in this state; I keep mine in my basement when not in use, typically about 68F. Fire risk tends to be higher when charging or fully charged, so I do the charging in the garage (away from flammable materials) shortly before use.
I’ve never heard about this before. I’ve always left them in the garage or the garden shed over winter, where temps can go to -30 C or lower. Never noticed a problem with the batteries when I’ve used them in the summer.
There’s a trope about Tesla’s catching fire (fortunately gas cars never do) which mostly relates to the earlier ones (as with Samsug phones). It seems battery manufacturing has been getting better over the years and manufacturers have learned what the problems are and how to avoid/minimize them. There are news items about electric bikes and scooters catching fire, but I don’t recall ever seeing anything about more ubiquitous lawn tool batteries catching fire, despite there likely being much more of them than scooters and hoverboards.
I would bring the batteries in - I assume they are the removeable type, you don’t need to bring in all your lawn implements. Maybe once or twice during the winter, set a reminder on your phone to charge them a bit so they don’t sit fully depleted for a long time. That’s what I did with my Ryobi power tool batteries, and only 2 out of 5 are dead now. (Actually, a common complaint with those PlusOne batteries)
People knowledgeable about lithium cells, please confirm or correct my impressions on this.
Don’t most battery fires etc. occur when the battery is either damaged or under electrical stress (charging or discharging)? It seems to me that an idle battery is the safest battery of all.
This video shows a raging garage fire caused by a battery. The main advice the fire chief gave was to not drop your batteries and to inspect them regularly for damage/cracks.
Gasoline and diesel cars can certainly catch fire, and not just because of fuel system leaks but also head gasket and lead-acid battery rupture. However, such fires can be extinguished with normal fire suppression means (Class B surfactant foams which smother the fire, making it unable to access atmospheric oxygen). Lithium-ion (and especially lithium polymer) battery fires, on the other hand, do not require atmospheric oxygen to sustain combustion, burn at much higher temperatures that will volatize standard fire suppression foams, and produce highly toxic gaseous products like hydrogen fluoride (HF), phosphoryl fluoride (POF3), phosphorus pentafluoride (PF5), and other toxic substances. The general guidance on fighting lithium-ion battery fires is to suppress combustion in materials adjacent to the battery and let the fire burn to completion, which can often take many hours.
Battery fires occur either because there are defects in the substrate or the electrolyte is breaking down. In good quality batteries, this should only occur under high load, and the power management system should detect when there is an abnormal charge/discharge profile and shunt around the suspect cell or module. In poor quality or counterfeit batteries (which is a more common problem than generally known), contaminants and processing defects can make cells far more prone to spontaneous combustion even under normal usage, which is a reason to not buy non-OEM replacement batteries from a questionable source.
Discharging batteries before storage to ~50% of capacity (and not charging to more than 90% or discharging below 10%) is more about extending the life of the battery by reducing the amount of self-discharge, but lithium ion batteries can and do catch fire in storage under no external load. Again, it is pretty rare with good quality batteries from a verified source but it can happen. LiFePO4 batteries are far less likely to spontaneously catch fire or even to break down under high loads, and are being progressively adopted despite the modest reduction in energy density they can store.
Not unless the batteries are only 50% charged when you take them off of the charger. If you want to get the state of charge down to 50%, you need to install them in the equipment and run the equipment. I did this a couple of years ago: I wanted to get my battery down to ~50%, so I put it in the mower and parked the mower in the backyard with a rope tied around the handle so it would run unattended until the battery was at a satisfactory state of charge.
The catch is that most fires in ICE-powered cars don’t happen while the vehicle is unattended in one’s garage. I’m uneasy about the prospect of someday charging a BEV in my garage overnight while I’m fast asleep.
True, and this is a liability issue for facilities providing charging stations in underground or structure parking. Some insurance companies are charging a large additional premium or refusing to cover damage from EV fires because despite how infrequent they are they can be highly destructive even compared to a gasoline fire.
If you were a bit of both, bored and handy, you could buy or build an appropriately sized cabinet, and install within it a thermostatically-controlled electrical outlet wired to a 60W incandescent bulb (you can still buy them).
