I’d rather have a single working headlamp than 10 flashlights. As such, I carry multiple headlamps. Flashlights have their place, and I tend to at least have a Nitecore MH20GT in the car as it’s USB rechargeable if you find yourself out in the woods and it’s dead. But a cheap Black Diamond Spot or 3 AAA battery Petzl is a better choice than the best flashlight I feel. I want my hands free to change a tire, set up a tent, wave my arms or whatever. I have a Nitecore HC30 that’s real decent. Lost trust in my Fenix HL60 headlamp when I found the battery run down after being fully charged but no use. Others have not had that issue with that headlamp. I like the Princeton Tec fuels (I think it’s the Fuel) as you they have a red feature as well, say if your car breaks down. If I know I’m heading out off the main roads into the deep woods, a Thorfire S70 flashight is a sweet thing to have in the car.
When I still had a car, I kept a TerraLUX Lightstar 80 (single AA, 80+ CRI penlight) with a lithium primary and a couple of spare cells. If I wanted to be snoopy while I was out and about, I also had a Rayovac 4V Lantern. And for emergencies I had an electronic flare. Since I always have a couple of lights on me for EDC, I guess you could say they were there as well. [Microstream, Tube, and sometimes my EA11]
I had an Olight R20 (18650 and micro-USB charging) but I’m not really fan of li-ion with extreme weather conditions…
The cold (–10°C) might discharge them and hot summer can be more than 60°C…
So I replaced it with a Thorfire TG06 (219C) with AA Ikea Eneloop (LADDA)
A Crelant V21A XM-L2 U2 flashlight (2)AA with energizer lithium batteries. Still works great after about 3 years.
In my truck I have my X40vn in the armrest compartment, the magnetic-tailcapped HO2 headlamp in the glovebox, and my flavor-of-the-day EDC, either an Eagletac D25A Ti, EA11 or the Mi7 Ti.
Ultrafire uf-10 with some spare lithiums. Zoomie flood and the magnet tail make it an ideal under the hood light. And you also have some throw when needed.
Very old zoomable flashlight from Aliexpress with new xm-l2 
I’ve got nowhere else to go. I don’t have the dosh to even buy a Convoy S2 without considerable pre-planning a full month in advance, let alone pack up and move. Third World will be Third World.
Sounds like you’d be a fan of Convoy’s head strap. It turns any tube light you may have into a headlamp. 
If I’m in the car I have my car keys which means I have a nitecore SensCR on me at all times.
I’m tempted to start leaving another light in the car for when I’m out and about. I think I’ll probably leave a TK75 in the boot as it’s sitting on a shelf at home just gathering dust so I might aswell keep something decent in the car.
I also have this in the car full time, with eneloops.
I avoid li ion in the car full time because of the high heat capacity loss problem.
I do keep a cheap Defiant headlight (100 lumens 3AAA NiMH) and a Coast Polysteel 600, 4AA eneloop, zoomie.
Also have cell phone with 50ish lumen flashlight and usually carry Convoy M1 as EDC.
So 3 lights full time and usually 2 other lights on me.
I especially like the “keep it to a minimum” bit.
The key for a vehicle flashlight is the BATTERY. What battery will be best able to deal with temperature extremes and be ready when you need it?
The battery technology that can best withstand the brutal heat and cold that a vehicle flashlight will be subjected to is lithium primary.
So, when it comes to flashlights that are left in my vehicles, I choose lights that can be powered by lithium primary cells, whether they be CR123 or AA Lithium primary.
And, ideally, that light will have quick and easy access to strobe mode, which may be very important in a roadside emergency situation.
Remember that Tesla is building a 18650 / 21700 battery with wheels that they call a car now days and they do just fine.
My cells that were in the car all last year still had 4.14V in them when checked a few weeks ago, and that was with a bit of use.
Tesla isn’t a fair comparison. Their “batteries” are made with a cooling system built in between/among the cells, as well as probably over/under voltage protection, overcurrent protection, and maybe a few other tricks we don’t know about. And they’re designed specifically to work in the vehicular electrical system that they’re a part of.
But even so, I’m sure you’re right that modern quality-brand Li-ion cells are safe enough to be left in a vehicle under most circumstances. I did have a Li-ion 18650 light in my car for a while. But, since I have the modded Mags that I can use with “D” primaries, there’s no reason to take a chance on what are really just old laptop pulls in my case.
The cooling system only cools the cells down to ambient temps at best. So no different then a cell in any other car (assuming it is not in direct sunlight obviously).
The cells are rated for temps of up to 80C+ in many cases, which is hotter then even the inside of a car in the sunlight gets except maybe in direct sunlight in death valley.
For fun a few days ago I gave one of these to a friend for in his black Mercedes ($13 on Aliexpress), and he just loves it! It even throws a decent spot with the 3x AAA alkalines, its angry blue fake XP-E led and plastic reflector. Btw, the build is really cheap, any attempt modding it is a bit wasted. For who’s into that, the weight and balance seems pretty good for wacking, but I expect it to break at the first hit.
His girlfriend was less amused by it
Pointers welcomed. Most everything available says “hardened steel” and I have my doubts about the claims.
I also have the LED “safety flare” things with lithium primaries in them, and a few real road flares as well.
This may be a dumb question, but I’m fairly new to the lithium game, but is it safe to keep 18650’s in a car in the summer? I realize there’s lithium batteries in Hybrids, but what if I left a light on my seat where it got direct sunlight on a 100°+ day?
I keep an old Led lenser without any circuit in my car with 3xAAA alkaline batteries because it never fails and i rarely have to switch batteries. Used it in +30C to –35C. If i need more light i can always use the cars.