which 21700 to choose prioritizing safety & cold/hot storage & use; no LFP cells available?

I’ve been using 18650’s for years but not an expert. Always purchased batteries from illumn or orbtronic based on recommendations here).

I picked up a couple cheap sofirn if23 (21700) floodlights for working on some outdoor projects. It gets pretty cold here (lows well below zero F), as well as some days over 100F in the summer. The batteries will be stored in an unheated shed, and it will be difficult/impossible to ensure what sort of temps they will be charged and discharged in. Further, they will mostly be charged with the sofirn’s built-in USB port. It’s not just me using them, and the family doesn’t care/understand nearly as much how bad things can go. I don’t want to burn the place down, so wanted to choose cells for safety >> capacity.

As such I went looking for an iron-based chemistry, but don’t see any.

Could you recommend a cell or three from a trusted vendor? How does safety compare across the available 21700 chemistries, especially for cells that will unfortunately be abused with deep discharges, sitting forgotten on a charger in the cold (or hot), etc.

Thank you!!

When I first got in to all this I tried to find the most inherently safe 18650 I could, and after researching the various different chemistries I concluded that the Samsung 25r was a good choice. The INR chemistry is safer than some of the others, so perhaps finding a protected INR 21700 might be good enough? I don’t know enough about lithium ion chemistry at extreme temperatures to guess how well they’d do in your case though. Perhaps someone who lives in a colder climate can answer that.

LiFePO4 is an iron based chemistry known for it’s safety. You can get them in the normal 18650/21700 etc formats, but you’ll have to check the voltage ratings to see if they will work with the driver. They will probably work (with less run time) while discharging, but the charging circuit might not be suitable (as it will try and charge them to 4.2 instead of 3.6V).

You could also consider NiMH cells in a different light, but that doesn’t really answer your question.

Welcome to BLF Roger :wink:

allow me to be blunt, no offense intended…

LiIon is not safe for your application.

It is dangerous to try to charge LiIon below freezing.

It would be a bad idea for you to put a rechargeable LiIon in a shed

where people who are unaware of the safety risk, could have the opportunity to make the mistake,

of trying to charge below freezing.

In practical terms, LiIon loses brightness and runtime, below freezing. When ambient gets up to 100F the charge in LiIon gets drained. So overall, LiIon is not the best choice for Cold and Hot weather storage.

I recommend you get some AA lights to put in the shed. With AA Ultimate Lithium batteries.

The USB rechargeable LiIon lights you bought, are the wrong tool for the job, and the brand of LiIon wont make any difference.

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Thanks for joining the gang, tungsten-filament!

Most liion cells are rated for sub freezing discharge temperatures, some even down to -40C, but none of them are supposed to be charged below freezing. So I’d say get cells rated for sub zero discharge temperatures, but charge them in a warmer environment. You can refer to cell datasheets for temperature related information.

As for deep discharging, it’s better to avoid that, so if your devices don’t have built in low voltage protection, get liion cells with an integrated protection circuit to prevent over discharge. I recommend the protected cells from liion wholesale. Here is a protected liion cell specifically advertised as a cold weather cell.

Lifepo4 is regarded as a “safer” and more robust chemistry and is not likely to cause a fire in any event. They are 3.2V nominal, so “direct drive” to a 3V LED works well with these, or a simple FET only PWM driver will work to provide modes and LVP. You can get Lifepo4 cells in pretty much all sizes. If you bought a large prismatic cell like EVE LF105 (reputable seller here) you would probably not need to charge it very often, since it has 105Ah capacity. Such cells can be charged with a hobby lipo charger or a benchtop power supply. RD6024 has an integrated battery charge function which means it has a setting to terminate the charge at a specific current. (charge current decreases as the cell gets full)