which 21700 to choose prioritizing safety & cold/hot storage & use

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

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I picked up a couple cheap sofirn if23 () 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 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 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 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 / 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

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

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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.

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. RD 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)

What is a Battery?

A battery is a rechargeable lithium-ion cell with a cylindrical shape and standardized dimensions of 21mm in diameter and 70mm in length. It was developed as an improvement over the battery, offering higher capacity, better energy density, and improved efficiency, making it ideal for high-power applications such as electric vehicles and energy storage systems.

Technical Specifications

• Chemistry: Like batteries, batteries come in various lithium-ion chemistries, including:
  • Lithium cobalt oxide (LiCoO₂ - LCO): High energy density but lower discharge rates.
  • Lithium manganese oxide (LiMn₂O₄ - LMO): Improved safety and thermal stability.
  • Lithium nickel manganese cobalt oxide (LiNiMnCoO₂ - NMC): Balanced energy density, power output, and safety.
  • Lithium iron phosphate (LiFePO₄ - LFP): Excellent safety and long cycle life but lower energy density.
• Voltage: Typically 3.6V or 3.7V nominal, with a full charge voltage of 4.2V and a discharged state at 2.5V to 3.0V.
• Capacity: Ranges from mAh to over mAh, depending on the chemistry and manufacturer.
• Discharge rate (C-rating): Some cells are designed for high-drain applications, offering continuous discharge rates (CDR) up to 45A or more.
• Cycle life: Can last between 500 to + charge cycles, depending on usage and chemistry.

Protected vs. Unprotected Cells

• Protected batteries: Feature an internal protection circuit to prevent overcharging, over-discharging, and short circuits, making them slightly longer than 70mm.
• Unprotected batteries: Lack built-in safety features and are generally used in battery packs with external battery management systems (BMS).

Common Applications

batteries are widely used in:

• Electric vehicles, with companies like Tesla and other manufacturers using them in battery packs for improved energy storage and performance.
• High-power consumer electronics such as flashlights, vaping devices, and power banks.
• Power tools, including drills, saws, and industrial-grade equipment.
• Renewable energy storage, such as solar power storage systems and backup power supplies (UPS).

Physical Variations

Some batteries come with slight design variations affecting their compatibility:

• Button top vs. flat top: Button top batteries have an extended positive terminal, while flat tops are flush.
• Protected vs. unprotected: Protected cells are slightly longer due to the built-in safety circuit.

As with any lithium-ion battery, it is essential to check the device manufacturer's specifications before using a battery to ensure compatibility and optimal performance.

If you are looking for more details, kindly visit Lithium Ion Cells.