21700 battery advice needed - BudgetLightForum.com

Someone correct me if I'm wrong but I don't believe there is a protection circuit in existence that will allow that kind of current flow through it. Seems like the max is about 10A, maybe a little more for some on larger cells like this? Come to think of it I don't think I've even seen a with protection yet although there are with it. Samsung 40T will get you there and I see a Sony VT6A I didn't even know about...based on the performance and longevity I'd go for the Sony (in fact I think I may order a pair right now), but it looks like HKJ is showing the Samsung to perform a little better overall in his tests. Last year I got the Samsung 40 and 50 for I think $7 but right now they're about $10, as is the Sony. They are flat tops and a true flat top which is actually very slightly recessed. I just received one of the 50E-2 from Liion which was a rewrapped version with their house wrapper and a "semi button top" they added (only ordered it because they were out of the standard factory wrapped cell). That semi button top is flat and it also isn't really raised like you might expect - just enough to permit series contact.

Standard Samsungs I have measure 70.8mm, the semi-button rewrap measures 71.5mm. I have a few Sofirn cells that say mAh and 40A on the wrapper (capacity is actually more than stated and they are good cells...not sure how they've tested for current but I kinda doubt they can do 40)...those measure 71.2mm.

If somebody has a protected cell then that should surpass your length requirements by a few mm, but you'd have to be sure it would fit, and also fit in your charger. Probably easiest to alter your light by soldering a brass button to replace the driver spring, and/or swap for longer springs. I would not try to use magnets to increase the length for this kind of higher current draw. Maybe a copper slug on the bottom end if you don't mind fiddling with that every time you open the light or replace cells but that would need to fit snug and stay snug. This is also a good case for the high current beryllium springs and a bypass wire mod if the light doesn't have either of those now.

Here's the IMR link for the Sony...they make you buy two, no onesies: https://www.imrbatteries.com/sony-murata-vtc6a--mah-40a-battery/

HKJ's handy comparator (select your cells from the drop down, pick your current(s) in the checkboxes)...he has other lists for small and large cells, NiMH, etc...and you can click on each cell you choose to be taken to the individual review and data: https://lygte-info.dk/review/batteries/Commoncomparator.php

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Been pondering this and I don't think I have great answers, but I do think this is worthy of doing it the right way and thinking it through carefully because we're not talking about a trivial amount of current. Are you modding/creating in a host, or altering an existing light, or just trying to save pennies on the batteries it was designed for?

Ultimately, it makes so much more sense to change the host parts in a way that they will take ordinary-length cells, rather than having to change each cell each time and attempt to get their lengths consistent.

If the tail spring board is easy to remove, totally try a longer spring there that can handle the current and retain all or most of its height while doing so over time. If that can/should be done on both ends, assuming the driver board is compatible and accessible, then do that...or perhaps a button/slug can replace a spring.

I really really do not recommend soldering cells. Spot welding is the way to go, when done correctly, but soldering adds a lot of risk especially on the negative end, and you need to add a considerable amount here, not just a little dab. If soldering is the way you want, then do it on the positive end/cap and be careful about it so you don't short, and quick about it so you don't damage seals or cause it to vent. Overheating the negative end can spell bad news for the cell either in performance or safety and that's true of these high drain cells that can take a lickin' as well as it is for ordinary lower drain cells that are somewhat more sensitive. And of course if you were to use protected cells then you wouldn't be able to solder on the negative end anyway. I've soldered buttons and blobs and tabs on dozens of NiMH and NiCd batteries over the years, but I won't solder lithium...did once, but all things considered it's not worth it to me unless it's just a blob on the top to make a small button but I haven't needed that in any of my lights in a very long time. I just wonder about all of the heat and current in this application. Plus soldering to nickel can be unreliable even with scuffing. We've seen springs literally melt from high current that was done wrong, and cells that overheated to a dangerous level through current or accidental shorts, so I wouldn't put a lot of faith in solder here even though their melting points are above what we'd expect to see.

I searched the forum for a bit but couldn't find posts that I think I'm remembering from the past about magnets and resistance/current limit. It may have been from Dale (DB Customs) in some thread, really can't remember. But I was thinking that there was a medium-level of current that was a practical limit for magnets but of course most who use them are using tiny ones as buttons/spacers, not thicker ones to fill up space and cover a larger cell. I would try some kind of slug to use as a spacer on the tail end if you don't want to modify the light itself. If nothing else, a copper pipe cap could be trimmed and filled with solder - a 1/2" is around 5/8" o.d. and I think a 3/4" will be too wide without a fair amount of sanding. I looked on Amazon to see if there were any convenient discs/slugs and there are lots of jewelry stamping blanks but most are way too thin - thickest I saw was 1/8" and they were pretty expensive for a smaller quantity of 10 or so. Washers and bushings present the problem of the spring going in the hole, so you don't get the effect you're after. If you have a very well stocked hardware store there are copper bolts that exist and you could cut the head off of one and grind it to suit....a little pricey but you could do the same with an electrical split grounding nut thingy. Heck, really for this purpose I think aluminum would be fine and if you can score a short length of 3/4" bar you could just trim pucks from it.

So the cost of parts and consumables, repeatedly for a trio of cells and more cells in the future, plus risks that are not zero...sounds cheaper and better to just spend a couple extra bucks on the ridiculously priced cells that fit the design of the light...and don't buy lights like that again. :)

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.

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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.

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