Overblown Concerns Over Li-ion Batteries Stored in Cars

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.


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.

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.

Just to add my experience, my aluminium-body gps unit turned from black to orange. Stored in dash. Same effect as when people bake their black flashlight. Imagine how hot it can be.

I also had a 70C thermometer burst in the car. This was long ago before temperature is hot as it is nowadays. Luckily it was the spirit one and not mercury.

Yup, but you are also in Malaysia, and you had to have parked in the sun, probably dash facing the sun for high exposure to get those kinds of temps. Also, you almost certainly didn’t have stuff in that glove box to insulate since the typical glove box contents would catch fire at that temperature.

There are risks, and everyone needs to take them into consideration and alter what they do based on common sense knowledge and environmental conditions. I would probably not leave a Li ion cell in the glovebox if I were living close to the equator, or even if I knew I was parking in direct sunlight during the summer here for hours. But here in WA for example all the risks are altered, I don’t face the dash towards the sun at the very least or park in the shade, my glove box is jam packed with junk including paper and plastic items that would probably burn, certainly melt at the temperatures you describe. In fact I have an “early warning system”: thin dog poop bags which start to melt/deform at lower temps, (I’ve placed them in front of a high powered light beam and started to get them to deform) and Ive never had them deform in the glove box. My cells have been fine for years.

But again I’d have to say don’t do it, and Id advise everyone who asked not to. You cannot know someone else’s conditions, situations, climates they are exposed to, habits or probability they would ever remember they even have a battery in the glovebox.

Even if we just forget the whole “hot car” argument, I know lithium primaries are better in very cold environments, and it is wise to have at least one light in your vehicle that can run on AA primaries in case of emergency.

Also good for years in storage, and they don’t alkaleak and destroy.

Malaysia doesn’t even get very hot does it? Isn’t their record, 104 degrees Fahrenheit?

That is pretty normal for summer temps in many American states.

Millions of Americans see 110 and 115 during summer, with records hitting the 120s.

Normal midday temperature is about 32-35 Celsius (up to 95 Fahrenheit) in the open over here in Malaysia, and sometimes it can hit up to 37-38 Celsius.
But bear in mind that this kind of temperature is throughout the year.

I’ve keep flashlight using 2x CR123 batteries inside my glovebox ever since I own my 1st car back in 2004, from Surefire E2e, Pelican M6 LED and now Fenix P3D without any problem. I also have a pair of new CR123 as spare in the glovebox too.
Recently this year I used to keep Jetbeam C8 powered by 18650 cell, with rechargeable USB but revert to the Fenix as the USB cable that comes with the Jetbeam started to deform when left inside the car.

That sounds plenty hot enough to to heat up the interior of a parked car. Park in the sun, and roll up the windows. You might not be cooking bacon, but you could still fry your buns.

My own choice mirrors yours. I would use lithium primaries.

The thing for me is that my car light is just an emergency light. I want to put it in my vehicle and forget about it. If I used Li-ion for the car light, I would want to carry that light with me when I parked on a hot, sunny day. That's a hassle I don't need.

We can argue this to no end and there will always be at least two camps involved. But the empirical evidence shows that within reason, LIon cells can be very safe and almost always are. Going from safe to unsafe can be a very long-distance jump which once begun might not be stoppable and that is worth considerable thought.

People learning to fly commercially are told that you start out with two bags; one is your luck and the second your experience. You can’t tell how much the first bag holds so you focus on filling the second one because if what you need is not in one of those bags when you need it, it’s all over for you. Don’t waste the first bag being stupid.

Above all don’t bash others who see things differently. Especially that.


Depends on the car and where the car is parked:
if you have a 100k$ car parked in a 700k$ house where you live with your whole family and a potential fire can destroy everything…it’s a bad idea

If you have a 500$ car parked on the other side of the street and you need a good flashlight in your car everyday, it’s another story.

As an emergency light which you actually never use, a flashlight with some lithium primaries or eneloops is the best bet. No risk and In case you need light you have a nice working light. That is why I have no 18650s in any car.

Actually your reasoning is completely backwards and shows classist misunderstanding bias: the people with the $100k car and $700k house have car insurance, good house insurance and good health insurance, whereas the guy with the $500 car has insufficient insurance for his house or family probably (if he has any) and would suffer more by such a fire :stuck_out_tongue:

But still, either extreme or anywhere in between, I would recommend against doing it. And using Lithium primaries is still better.

Don’t rely on the assumption that your car, home, and fire insurance are going to pay for losses.
Not that anyone would be intentionally careless because they’re insured — right?

If the insurer’s lawyers can argue you were careless, or used something wrong, or used non-brand-name equipment, you may not be covered for losses that they can attribute to lithium-ion batteries — remember this isn’t about what you did, it’s about what they can claim you might have done.

There is a LOT of expertise being dedicated to denying claims for fires attributed to lithium-ion problems.
Here’s a discussion of how the lawyer-them-away approach to claims is done, by lawyers who do that kind of work:

It always comes down to the same thing:

Do ya feel lucky? Do ya?