Overblown Concerns Over Li-ion Batteries Stored in Cars

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? :~

Venting is not supposed to do that, it is a safety feature.

But the vented gases are flammable and if the light makes a spark when the pressure raises, you probably have an explosion.

Oh! Thank you very much HKJ! The more I learn new things, the more I realize that I still have a lot to learn. :bigsmile:

And remember, if it vents, don’t inhale.

If you’re driving at the time, stick your head out the window.

Woof.

I’ve kept lights with li-on batteries in my cars for years in Southern California heat and I’ve never had problems with the batteries. Not sure if I’ve just been lucky so far.

Most of the time a cell would vent not explode, I think an actual explosion needs a lot of other factors (closeby material to ignite, enclosed space to trap pressure that fails, etc), venting is what the cell is meant to do under pressure as a safety feature.

Ah yeah, what he said :slight_smile:

I have 6 4.35v cells I keep at 4.2v for emergency

I got them from a laptop pack for $9 on ebay

I also have about 10-20 cr123 and 50 eneloop AA for emergencies

I have a few home made solar spotlights mounted under the eaves. I live in Mohave Valley near the Colorado river, we see temps in excess of 127 Degrees F during the summer months. The Lights are built in standard Electrical boxes and are charged daily. I have some with Tenergy 26650’s (2) and Panisonic 18650B’s (4) and most have survived outside 2 years now. I had one get water inside and had to replace the charge boards. So after 600+ charge cycles I would say that leaving them in a car wouldn’t be too much of a problem.

I’ve been using cheap temp/humidity data loggers for a while and it’s been rather surprising to see actual data for shady outside wall versus attic with different roofing material versus cars. Worth a try in your location. Direct sunlight is surprising.

Is it just me but all this talk about temp has me thinking that the single largest source of hi temps getting to the batteries is, in use.

What temps are folks seeing for their cells while in use?

That is probably the most likely time to vent etc.

This may be a bit extreme, but it’s one example:

“I found the light got VERY hot after a short while on high mode. I guess this is somewhat expected… but while it was left tail-standing in a warm room for 10-15 minutes…it was literally TOO HOT to pick up! Again, this was on high, not ultra-high. A temperature reading of the bezel after I shut it off, exceeded an incredible 1000°F!!”

Reference: Shadow JM35 Review w/CREE MT-G2 -

So, it’s no wonder that UL and IE standards call for testing of Li-ion cells to 266 degrees F.

I’m a dash-cam-aholic as well as a flashaholic, and those really take a beating from the summer sun and heat. They use LiPo bag cells and many are reported ‘puffing’ in extreme heat, so those who use these in extreme climates have learned to take the cam out of the bracket and store it when parked. That’s usually in the dash. I can’t recall ever hearing of one single instance of a puffed battery from being stored there. Guys have ran extensive tests with temps in a car in different locations and the dash (glovebox) is generally the second coolest location of a car interior; under the seat being the best. Car trunks (boots) vary but again are not a problem with dash-cams and their LiPo’s. The absolute hottest place in a car is atop the dash in direct sun and at the top of the windshield below the tinting in the direct sun. You’re not going to have your flashlights there.

Yes, heat is bad for a lithium cell-battery. Yes, it can kill them. Yes, it can lead to fires. Yes, cheaper cells are more likely to have problems. But it’s only in extreme situations where this is a catastrophic danger. Rechargeable Lithium batteries and cells are designed to vent safely, but flashlights are not. Dash-cams are plastic so they yield rather than burst, but metal flashlight bodies won’t and this has happened enough to show that you should be concerned about it. With flashlights and cells stored in the dash, the trunk, or under the seat you shouldn’t have a serious problem but it may shorten cell life. Best safety will be with cells separately stored out of the light in a fireproof enclosure.

Good to be concerned- that will lead to you becoming educated to the dangers and not making mistakes due to ignorance. Bad to be paranoid- that will lead to you making mistakes because you’re not seeing and understanding clearly. Worst to be stupid- that always leads to problems.

It gets fairly hot here in the summer. I have LiPo and LIon’s stored out of direct sun in my vehicle. I’m watching for danger signs but not worried. If it does burn my vehicle I’m going straight to the store to buy a lottery ticket because it’s going to be a very rare kind of day indeed.

Phil

Yep. I’ve had two of those puff up like golf balls, almost spherical — both of them were in solar-charged battery boxes, the widely sold cheap things with a large and medium or small USB port and a few LEDs. Broke the boxes open.

Good thing there were no sharp edges in contact with the bag cells when that happened.

Sometimes I figure China’s secret plan to conquer the rich West is to distribute their batteries worldwide.
Then one fine day their secret satellite signal gets sent that triggers them, and makes them all explode at once.
Conflagration.

I have kept Li-ion cells of various types, sizes, and brands, in my work truck, ever since I have used them (about five years). I normally keep them in the glove box or center console in backup flashlights and in storage boxes. I have had no problems because of the winters and summers of Oklahoma. We have many days of over 100 degrees F during the summer and usually many days of single digit cold during the winter.