Overblown Concerns Over Li-ion Batteries Stored in Cars

I was reading this post and came across a few comments recommending against leaving li-ion powered flashlights in cars due to the hot temperatures that arise in the car during the summer.

From what I’ve read on the subject of single-cell flashlights, the fear of fire, explosions, or venting due to the batteries being baked in the car is not warranted. Temperatures are not high enough to induce these problems. What does happen is that:

  • High temperatures are not the ideal storage condition for batteries, so they will lose their charge more rapidly (35% per year @ 104F).
  • Li-ion batteries don’t like to be stored at 100% of charge, so using them for emergency purposes leaves you with a dilemma. Store them partially charged (say 4.0V), but you won’t get the maximum run times when you need it in an emergency. Store them at 100% and hurt their long term performance. Or switch out the batteries periodically, so that they aren’t sitting around so long.
  • Primaries are usually cheaper than rechargeables, so it’s a waste of money using a rechargeable battery for such purpose (assuming, of course, that primaries are available to do the same job).

I don’t recall any discussions about multi-cell flashlights.

So, what are your thoughts about the subject? Yea or nay to the practice of storing flashlights with li-ion batteries in the car?

. . .

I’ve suffered fires in my car twice. The first time was when I pushed in the cigarette lighter and it didn’t automatically pop out, causing a small electrical fire. The second time was when a gas station attendant forgot to replace the oil cap (the engine was extremely hot from being driven from N.Y. to Miami), causing an engine fire. Haven’t had any problems with my flashlights stored in the car, though!

Well, other than dead batteries, that is. 0:)

Say what you will, I’ll be paranoid. I won’t leave an 18650 in car that could go over 130f. But that’s really only a small part of it.

In terms of a flashlight needed for emergencies, it just doesn’t make as much sense as lithium primaries. Not only do primaries do much better in cold climates (not a problem in Hawaii), but if you’re ever stuck in the middle of nowhere or during a major power outage, you can find AA’s in almost any farmhouse or convenience store. Good luck finding power and time to charge your 18650’s every time they are low. Lithium primaries have a great shelf-life as well.

Like I said in the other thread, if I know I’m going to need extended use of a light, I’ll bring a rechargeable with me. But anything that is permanently in my car uses primaries.

interesting theory!

what about mobile phones and laptops and tablets?

I always have my EDC on me. my xtar wk21 and a Nitecore tube and it get hot here in australia but they are in a bag maybe that helps i also have two spare 16340’s on me

I can see concern i guess if its left in direct sunlight through a window on a really hot day because the body of the light will heat up also… but one of my cars i have a lithium battery in the boot that runs the car because there was no room left in the bay with engine upgrade.

what about hybrids and full electric cars?

I guess its all about placement but i do have a AA light in the glove box if needed it has different colour led for emergencies…

I had a nokia phone battery puff up from leaving it in the car in summer. Was 49°C/120°F in the shade, can’t imagine what the temp would have been in the car that was parked in the sun.

It could have been a coincidence, but I no longer leave any portable batteries in my car in warm weather.




  1. Don’t do it, it is a risk, they can explode.
  2. I do it anyways…wait, ignore that, re-read #1 :wink:

The reasons I tend to ignore #1 are:

- I live where it rarely gets too hot.

- I rarely park where the car sits in direct sun if it was hot out.

- I crack my windows when I leave the car.

- I think the glove compartment with my assortment of junk has some level of insulating capacity even if the above ever fails.

  • I use laptop pulls so that if their life expectancy is reduced, I don’t really care.

But still I’d say don’t do it, I couldn’t recommend it. I can’t even be sure I’ll do exactly as I say, how can I be sure you will?

who needs car when my old nokia phone battery inflates and burst into flames just by direct malaysian sunlight here.

yep I forgot to take my phone by leaving it on a park bench. I came back just to see it liquid black melted

In that case I consider myself lucky I left it in the car, not in my pocket and that it only puffed up.

:smiley: :bigsmile: :stuck_out_tongue: :slight_smile: :stuck_out_tongue: :bigsmile: :smiley: :party:

There are many documented cases of cell phones spontaneously catching fire, so I can see your concern about your cell phone. And manufacturers have worked hard on that problem, so I’m not sure how much of a risk it is at this time.

However, I have been unable to find any cases of car flashlights spontaneously combusting.

I found one instance of a battery catching on fire while being recharged in a car, but I’d never advocate anyone charge their Li-ion batteries unattended - much less in a car! :~

Anyone concerned about leaving the flashlights in the car should avoid buying any hybrid or electric vehicle. There are many more cases of car battery fires than of car flashlight fires.

Of course, this may be a case where statistics lie. The number of people with car flashlights may be much smaller than the number of people owning hybrid or electric vehicles. Moreover, the people who experience a car flashlight fire might be less likely to report the fire than people who experience their car battery catching on fire. Lastly, it is much more likely that the car battery fire would rise to the attention of the media to publish the report.

Heat is not the friend of electronics devices or batteries. Li-Ions may not explode solely due to heat in a car, but it’s not good for them nonetheless.

I store a LOT of lithium ion powered flashlights in my van. I’m just careful where I place it and I seldom park my van under direct sunlight. Been lucky to be incident free (i.e. lithium ion problems) so far but if the experts here could chime in and explain why I should not do it then I’ll be very willing to oblige.

I however have an experience with battery venting and this happened to my TrustFire X100 while displayed inside my Flashlight Curio. No I did not hear any explosion nor seen any smoke come out and no, my curio is not hotter than my van parked under the sun.

I just observed a few days ago that my X100 was dim when I played with it prior to modifying it. When I opened to check its batteries (3 King Kong 4000 mAh 26650s), I noticed that the middle battery had white discoloration (as if left there by thick white smoke) in its anode and its plastic cover surrounding the anode have partially melted. The cathode of the battery in front of it also has the same marking and I could only speculate that the middle battery vented silently while the X100 was on display.

My speculation was reinforced when I took the DMM readings of the 3 batteries. The first and the third batteries each read 3.95 volts and the middle battery read 0.00 volts. When I made a quick test using my Opus BT-C3100, the said battery won’t register anything - it was totally dead.

So I suppose my King Kong 26650 vented - and nobody even noticed it. It just vented silently and except for the white markings on the battery in front of it (which was easily wiped out with damp cloth) it did not cause in damage to the other batteries nor to the X100 nor did it cause fire or explosion. So if the experts here could chime in and explain why I should not place flashlights with lithium ions inside my van (I could just be very lucky so far) then I’ll be very willing to oblige. :slight_smile:

Lithium-Ion Batteries Hazard and Use Assessment Link

From page 12:

A number of studies have attempted to rate the “safety” of different positive electrode materials.15,16 These studies are based on thermal stability measurements of the cathode materials with electrolyte at full-charge voltage conditions. These tests show that cathode materials begin to react exothermically with electrolyte at a range of temperatures from approximately 130 to 250°C (270 to 480°F). Safety rankings based on this data have been strongly criticized in the industry because they relate to only a single aspect of cell safety: the reactivity of the cathode. They do not take into account the many other factors that contribute to cell safety such as the reactivity of the anode (which usually begins to react exothermically at much lower temperatures), cell construction details that may affect the likelihood of developing an internal short within the cell, the probability of manufacturing defects to cause internal shorting, etc.

Page 14

As temperature increases, reaction rates between the electrolyte and lithiated carbon increase exponentially (following Arrhenius behavior). Thus, lithium-ion cell capacity fades and internal impedance growth accelerates with increased ambient temperatures; most lithium-ion cells are not designed to be operated or stored above approximately 60°C (140°F). Many soft-pouch cell designs exhibit swelling if operated or stored at 60°C or above, due to gas generation from reactions similar to those responsible for SEI-formation.
For most commercial lithium-ion chemistries, the SEI layer itself will breakdown when cell temperature reaches the range of 75 to 90°C (167 to 194°F; exact temperature depends upon cell chemistry and SOC). Accelerated rate calorimetery (ARC) has shown that commercial lithium- ion cells exhibit self-heating behavior if brought to a temperature of about 80°C (176°F).22 If cells are then maintained in an adiabatic environment (e.g., if they are well insulated), the cells can then self-heat to thermal runaway conditions (this process requires approximately two days for an 18650 cell tested in an ARC). Note that United Nations (UN) and Underwriters Laboratories (UL) tests for lithium-ion batteries discussed below require cells exhibit long-term thermal stability in the range of 70 to 75°

Another google search turned up research indicating cabin temps can get to 20C above ambient when parked in the sun so I guess risk level depends on where you live and park the vehicle.

Thank you for providing the link to the document. :slight_smile:

There’s a lot of disussion about the chemistry of the cells, but little in the way of empirical testing or case examples to prove the theories.

The only test cited where overheating caused a problem was under “State of Charge” heading on page 70: “In testing one commercial cobalt-oxide cell model, the researchers found self-heating onset occurred at 80°C (176°F) for cells at 100% SOC, and at 130°C (266°F) for cells at 0% SOC.”

The lack of supporting documentation can be taken in two ways, (a) it hasn’t been a problem or (b) not enough research has been done on the problem.

And I’m not sure what to make of the testing criteria on pages 38-39:

Similar temperature tests are listed for IE Standards. I’m not sure if these are special tests for high endurance qualifications, or whether all batteries are so tested. But the test criteria are quite high (266F!).

Most LiIon batteries are run through this type of test (Cheap Chinese probably not), just be aware that the battery do not have to survive the test, pass criteria is usual "no explosion and no flames", i.e. venting is accepted.

Thanks, HKJ! You are a vast library of information.

And easily accessible, too! :slight_smile:

Which means that venting does not necessarily lead to explosion and/or flames? :open_mouth:

In that case, the ‘explosion proof’ features of aircraft grade aluminum flashlights should be enough to prevent fire inside cars caused by lithium ions. I guess the best thing to do then is be very careful where you place your lithium ion flashlights while inside your car and where you park your car? :~