For an emergency use or little use which type of battery should i use?

If i want an emergency light for leave it inside the car, which kind of battery should be recommendable? I mean, you can’t leave a 18650 or a NiMh battery inside the light. I don’t know about the consequences but, seems not recommendable do that.

On the other hand, what if i want a keychain? I carry on with me everyday but the use is for specific moments. Would it be convenient leave inside an AAA/AA battery? Should be better an USB rechargeable battery like we do with our smartphones? What specific name have this kind of battery?

A good quality li-ion like an 18650, 14500, 18350, or 21700, kept at around 3.6v will hold that charge for a long time. It is not remedied to leave a nicad, alkaline or nimh in a light (or anuthong) with potential parasitic draw because it can cause the batteries to leak. A nimh like an Eneloop or something similar thats low self discharge will also hold a charge for a while. Some flashlights have built in batteries, but enthusiast grade ones usually don’t.

Maybe the solution to leave an EDC inside the car is to unscrew the tail, not to cause some problems if it is inside the car for a month there, without using and with a 18650 inside the light. Is this correct?

What about a keychain light, you use for specific few moments? I suppose you can’t just unscrew the tail, maybe the light could fall to the ground.

It gets so hot here in the summer, I don't think it would be a good idea to leave a flashlight with batteries in the car.

I EDC four different flashlights, so I just use what I have on me.

(Only one of the flashlights is impressive.

The other three are just backups in case the battery dies.)

I carry 2xAA lights in both cars. NiHh to be more exact. Have had them in there for years now with no problems. They see the extremes in the winter as well as the summer. I top them off once a year unless they are used and required more charging. I have never had a single problem. Don’t know if this would somehow degrade the cells after wards but I haven’t seen anything that would make that statement true.

If you get good quality abtteries they won’t be as delicate as you think they are.
A typical nimh, alkaline, or li ion can survive pretty hot or cold temps.

energizer ultimate lithiums in AA/AAA sizes and CR123A (ones made in the USA) are the best way to go for a light kept in a car. These will work in extreme temperatures, both hot and cold and they don’t leak.

Alkaline batteries are very reliable, just replace the batteries every 2 or 3 years to prevent them from leaking if they are not used.
I have a 4x AA headlight in the car, it will only be used for emergencies, and i replace the alkaline batteries every few years.
There is a piece of plastic between one of the contacts of the batteries to prevent them from draining (that headlight has an electronic switch and there is a very small current drian when it is not used).
I use these and never had problems with leaking cells:
https://lygte-info.dk/review/batteries2012/Aerocell%20AA%20UK.html

These Aerocell AA are only 1,99 Euro for 8 cells (Lidl).
So it is only 1 Euro for every 2-3 years that the headlight stays in my car next to the spare wheel.

Absolutely disagree with leaving an alkaline battery in any kind of device for long periods, especially devices subject to extremes of temperature. I’ve simply had way too many leak and destroy the device.

Primary lithium or CR123A would be my first choice. Huge shelf life, decent output, very little chance of leaking.
2nd choice is a good quality LSD NiMh. It will suffer a bit in the long haul due to less than optimal care but that’s just part of the price.

LiFe lithium is lower voltage but pretty robust. Some lights might be just fine with that.

I think your choice of lights is about as critical as the battery for this application. You want simple, robust, without parasitic drain.

I was just curious , because i know all of us have an emergency light inside the car. My question was about how they do, considering that is not convenient leave batteries inside the flaslight.

·How work Primary lithium, CR123A and LiFe lithium?. Do you have to charge them like any other 18650 or Nimh?

·I would appreciate some recommendation of battery for a keychain that i would use for few specific moments. I was looking for some usb rechargeable battery. I would choose AAA/AA if there is no any danger considering the Nimh would be inside the flaslight for a long time due to my use.

Thanks!

Primary means non-rechargeable lithium. Use them just like alkaline, but they have a much longer shelf life and are not likely to leak. I use them in things like smoke alarms, thermostats, and some remotes.
CR123A is higher voltage lithium primary, same diameter as a 18650, but about half the length. This kind of light would work well if you wanted a tiny light with better output than AAA. I see not problem keeping them in a car. They are often used in photography where you could ruin very expensive equipment if it leaked.

LiFePo4/lithium-ion phosphate is a type of rechargeable lithium, a bit lower voltage (3.3v) and lower capacity, but is more robust than Li-on. Some people don’t think it’s a good idea to leave Li-on in a car….just in case.
I have a few LiFe from an old use but not sure I’d go out of my way to get them. LSD NiMh is probably more generally useful.

I have a small AAA twisty with a NiMh eneloop that’s easy to get at in the car for regular use in the dark. I also have a AA NiMh eneloop headlamp in the trunk if I have to have hands free and do some work that will take longer or need a lot more light. NiMh are very unlikely to leak. They will slowly discharge so it’s reasonable to pull them out and cycle them 1-2x/year. Decent batteries should still last a long time. Only use LSD NiMh for this, otherwise they will be discharged when you want to use them.

Primary batteries aren’t rechargeable. You throw them out when discharged.

I think for the moment i will go with the NiMh for Keychain and emergency use inside the car. Maybe further in time when i know more about CR123 batteries i’d try.

For the NiMh AA i know Eneloop and Ladda. For the AAA option are there any good options?

Thank you so much for your help!

For AAA size NiMh again the choice is Eneloop or Ladda. Maybe regular Eneloop is better than Ladda (or the equivalent Eneloop Pro) for this purpose, because they have less self-discharge.

I use lights with CR123A or AA lithium primaries in my vehicles, as recommended by several earlier posts.

Some flashlights that are standard with a single 18650 Li-ion cell will also take 2x CR123As.

It has been stated, for many years now, that lithium primaries are the best choice for leaving in vehicles for extended periods of time - thus, that has been my choice… for many years. Otherwise, I use Li-Ion rechargeable almost exclusively. With Eneloops in the few lights I have which aren’t able to handle Li-Ion.

I have an AAA light in my car, loaded with Eneloop
I have an AAA light for my keychain, also loaded with Eneloop.

every few months, I change the battery in the car light… I have never had the light not work. It stays there during freezing winters, and hot summers.

It would be better if I used 1.5 volt Lithium Primaries, for example Energizer Ultimate Lithium, but those are expensive, and not rechargeable. That makes me reluctant to actually use the light…
They are the best choice for an emergency light left unused for years at a time…

I prefer rechargeable AAA or AA Eneloop. In my practical experience, they work even if left in a hot or freezing car, long term. With appropriate battery changes periodically.

I do not recommend leaving any 3.7volt LiIon in a car, that means no 18650, 16340, etc

I use lights with 16340 batteries for the majority of my needs, but IF I was going to leave one in a car long term, I would change the battery to 3 volt Lithium Primary, called CR123.

It is a BAD Idea to use lights with TWO CR123… Lights that use only ONE battery are safer.

This, absolutely, when the earthquake shaking stops and you really need a working flashlight, those will be the ones you reach for.

Once you sort out the chaos, your NiMH will sustain you and the neighbors for a while — assuming you have a solar panel and big 12v battery, or a car power plug, and some battery chargers handy that it will power. Oh, and the usual advice, never let your vehicle’s gas tank fall below half full.

Are there examples of a problem with a single battery 18650 flashlight in a vehicle because of high, low temps or length of time? I’ve searched in the past and I can’t find them.

What I have in my cars is an AA flashlight ready to use with a LSD NiMH, and 2 separate alkaleaks AA as backup in a zip-lock bag. Cheap as hell. Once a year I top up the NiMH and check the alkaleaks to replace them if have leaked or have low voltage (very rare). They withheld temperatures of >50 C in the summer without a problem. Wouldn’t feel comfortable doing that to any li-ion battery, not even primary ones.

missGoogle told me primary lithium has a bit wider temperature range than eneloop:

The Energizer® Ultimate Lithium™
(–40ºF to 140ºF).

Eneloop
(–20ºF to 120ºF).

I believe cars can get hotter than 120F… depending…

but yes, eneloop works fine in my car, in my real world
mild winter temps of 20F
pleasant summer temps of 80F

have never put a thermometer in my car… where my flashlight is… hmmm more corona time entertainment…

you made me look… lol

maybe 18650 are not going to blow up in a car: