On testing and recording temperatures, I'd use an inexpensive weather station with indoor and outdoor sensors. These typically reset in 24 hour intervals so you can capture max/min temp.
I think you'll find the temperature to be consistent throughout the interior but out of direct sunlight.
I have a somewhat insulated fold-down middle front seat with storage that if anything, just delays an equalization between its' interior and general vehicle interior.
From experience, I have tested a crapfire battery that was left in the door pocket of a Tundra and its' capacity diminished from 2500 to <200 mah. I was familiar with the battery capacity before it went through about 2 years of these conditions so I have some idea of if it was an ok battery.
In the southern US, I will keep a lithium powered light in the vehicle during our so called winter and switch the light to one that can use lithium primaries, ie. Energizer Ultimate.
A 3 C cell light can have a conductive but insulated spacer to accommodate an 18650, 21700 or 26650 battery.
Even here in NYC (not exactly tropical climate) I tend to leave the windows open a bit in the summer so that I won’t be getting into a toaster-oven.
As far as anything with batteries, Just Don’t.
I had cheepie plastic-tube flashlights with D cells that leaked and subsequently petrified. Easy to just toss the whole thing.
“Better” flashlights like Mags back in the day, nope, same dealy, those hateful little alkaleaks did what they do best: ruin anything they’re put into.
Anything Li-ion? Nah, I’m allergic to car-fires, especially if the car in question would be my own. I’d always take “dashcams” (suction-cupped to the windshield, actually) and GPS thingies with me rather than leave them inside.
My “car-light” is whatever light I’m EDCing on me.
Gun-to-my-head, I’d only use primaries like ’123s in lights, maybe eneloops if I needed something rechargeable. The latter tends to be pretty resistant to temperature extremes.
Hello from the Florida swamp. 105 degrees in the shade.
Never have had a problem with Li-ion.
I have around four 26650 in the car all the time.
2 lights and two eCigs.
The coolest place is the glove compartment.
Althought I carry in the console also. Bad place.
However, I drive a light pearl white car with Heavy tinted windows.
Tan interior, including the steering wheel.
The windshield also has a newly developed film for UV rays and heat.
You can place your hand on the hood at three o’clock in the afternoon,
and not feel any pain, with the car cold.
I look for shade when I park. And open the sunroof to the front.
Not because of the batteries.
But because of the driver.
Good luck with a black car here.
I also live in paradise (Florida) and have left mine in the car also with no problem.
Red car with black convertable top.
I do leave the windows cracked a couple of inches.
Lights are s43s with a 18350 and a blf a6 with a 18650.
To add some additional perspective, most cars aren’t EVs, but they do carry ~10-20 gallons of volatile, flammable liquid, which, in a late model example is injected into a big hot metal lump at 2000+ psi (compared to ~10-50psi in days past, over the entire path of the storage tank to the pintle). Said lump also likely has a smaller lump hanging off of it that glows red hot when in operation. Underneath the car is a metal canister with a ceramic/precious metal core that exceeds 1000F when in operation, with an external housing temperature of several hundred degrees, even though it’s double-walled, in proximity to lines carrying said liquid from the rear of the vehicle.
All of which is subject to breach in a collision, and doesn’t vary in relation to environmental conditions.
That said, I have swapped out an old, cigarette-outlet powered light that was large and unwieldy in favor of a small tube light that will handily outperform it, using 123 cells.
And if any of the above goes awry, that’s what the extinguisher mounted underneath the front seat is there to help combat.
Good to be mindful, but also see the bigger picture. There are so many devices powered by Li rechargables nowadays, outside of lights, that are used with no consideration or special handling whatsoever. Where does the worry begin and end?
Unless it’s straight up mechanical, I wont modify a light in case I screw it up.
I have expensive cars, not because money grew on trees, but because I will buy a daily runner and keep it for a decade. Sports cars for two decades. I love cars and try to keep them in immaculate condition….which does not include picking up smoking parts from the street.
Up till I joined this forum, I never thought about flashlights and fires. I just replaced the ni-mh batteries every three months and went about my life.
Anywho…….I found temperature reading strips. 10 pieces for 20 bucks. I’m going to wait for the higher temperatures, toss them in the 4 areas and see what I get. The upper range is 170F, if it get pegged anywhere near that, I’m going back to ni-mh for the cars.
Queensland Aust.
Tropics. Av temp’s around 34/37c in our “summer”
I have a torch in each car. Drivers door pocket. 18650 cells.
Shorts. T’shirt and sandals weather all yr round, apart for a month or so with a skivvy on in morning. (Our “winter”) Even out rain is warm. never ccold.
We do get up to 41/41c a coupla times a yr.
Never had a problem. So far.
Pull them out every 6 months or so for a charge.
BUT. I wouldn’t use those Chinese battery’s.
LG and Samsung only in mine.
Tempil makes all sorts (irreversible) temperature-reading strips, but dunno if they sell in small quantities. Could be 1-4 different values per strip.
They also had “crayons” of a sort, which’d permanently change color once a certain temperature would be reached. So you’d draw a line or write a number or whatever, on, say, a differential’s case, and if the marking would change color, you’d know it hit a certain maximum temperature.
I used temperature strips a long time ago. Just forgot about them.
I had a massive claim of product delamination from a good customer. It was impossible…until we started focusing on the trailers. Apparently they reach close to 170 F in the southern states. The trucking company claimed it was “impossible”…until we put strips in the trailer. They paid up……
I also started using a catalyzed glue in the summer.
Point is that there are easy alternatives. Lots of nimh lights available that out 1000 lumens.
Hot? Le’me show you hot.
Taken outside my office building a few years ago.
Any yes you can cook an egg on the pavement.
Laptops full of 18650s have lived in cars for summers on end.
Cop cars have them on mounts in full sun.
Some of the oilfield trucks out here have the same sort of setup.
Don’t know if any have had problems.
Laptops tend to have very high quality batteries that are run within “conservative” specs.
Somewhere I have a temp. datalog from inside the central consul of my car. It’s been a few years but I think it maxed out at 135. Not nearly as hot as the inside or dash temp. If I find it, ill chime in again.
And it’s already been over 90 here several times this month.
Not looking forward to summer….
I don’t know about Li-ion cells —But several years ago here in La. my daughter left a Bic lighter in her drink holder middle of August—- around 2:30 the Fire Dept was called —it had exploded causing her car to go up in Flames
NASA paid for a study just a few years ago that you can find in PDF form. It’s worth reading but I’m not going to link to it. Seems it’s mostly about how safe it is to transport some of their spec battery packs here on Earth. Edit Nasa has done quite a few studies on 18650 cells. The one that I read is about thermal runaway. Search for “NASA 18650”
