Picking the right 18650 batteries and charger, some specific questions from a newbie

Hi all,
As I said in my recent introduction post, I have a fair amount of experience with AA/AAA pocket lights but have been looking for a larger light that has more juice and runtime capability–something that I will likely put in a backpack or jacket pocket when out camping in the woods for multiple days or perhaps use if we have extended blackouts.

I recently ordered a Convoy S3 (519A, 4500k) to test out in that role, after I heard nothing but good things about Convoy and Simon’s Aliexpress shop. It only cost me about $6 extra bucks to add a battery and charger to the order after getting a first time purchase promotion, so I went ahead and did so. However, I don’t know if the add-on battery and charger are going to be good longterm solutions for me.

Let me say that I am not well versed in rechargeable batteries. I do have a couple of rechargeable lights, but I got included batteries and they charge via a port in the light so I don’t need to use a separate charger. Therefore, I have never needed to pick out the right battery and charger to pair with a given light.

First off, the charger: The deal I got was a Yonii TC1 for $0.99 which I figured would be enough to get me started. However, I started doing a little reading after it shipped and it sounds like some of the cheap Yonii chargers have a problem with overcharging. At least it has definitely been reported for the Yonii Q1. Can anyone comment on the TC1 that comes from the Convoy Aliexpress shop and whether or not it overcharges? If so, I probably need to acquire a new charger pretty shortly. In that case, what should I look for in a charger? I have some general understanding that the ampere rating of the charger relates to charge rate, but other than that I have no idea what specs to look for with regard to what makes a “good” charger. Also, if I use the cheap charger for the time being and it does overcharge, does that risk damaging the light or simply damaging the battery cell. If it overcharges to a slightly higher voltage than it should, then what are the potential consequences?

Secondly, the battery. It appears to come with a LiitoKala 3500 mAh Li-ion 18650 cell. From some general internet browsing, I know that 3000-3600 mAh is pretty common for 18650 cells. That spec is fairly easy to compare. What I’m not so sure about are the other specs: flat top vs button top? Protected vs not? In addition, I started looking at Vapcell batteries online, since I had heard good things about them on the light forums. That just confused me, because Vapcell apparently sells a bunch of different 18650 lights that have different ampere ratings (10A, 20A, 18/35A, 8/15A, etc…). And what about 18650 cells that just have the usb port built into the cell for charging? I have some rechargeable 14500s that just plug into a USB-C charger. I have seen at least one 18650 cell that charges similarly. Anything I need to know about those? In general, what do you look for when choosing a rechargable 18650 cell?

Sorry for the barrage of questions. I just want to feel like I am making informed decisions and not just buying the first thing that pops up in the search engine. Thanks for any insight you can offer.

Most chargers tend to use variants of the same IC in the same circuitry, so chances are really good it’ll work fine.

And “Genuine LK” cells are rewraps, often from decent mfrs like Lishen, so I wouldn’t worry.

Invest in an analysing charger like an Opus (got a bunch, but the Ope is my go-to) so you can measure capacity. If it clocks in within 10% of what’s on the label, it’s fine.

(“Genuine LK” on 18650s is like “Famous Ray’s Pizza” in NYC.)

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I have a Yonii charger. Think I got it from CountyComm a few years ago. I used it for travel. I’ve caught it charging a Sofirn 3000 mAh 18650 to 4.23V, so I don’t really care to use it anymore. Now have an Opus BT C3100 V2.2. I like it, but it’s too big to haul around. If I’m on the go, I tend to pack pre-charged cells or lights with on-board charging that I trust. Personally, I stay away from cells with built-in charging circuits for a couple of reasons: A) they tend to be abnormally long, creating compatibility issues size wise with some lights, and B) suffer from parasitic drain due to the circuit monitoring. Plus most forfeit some capacity to accommodate the additional circuitry. Ditto with protected cells (I have and use a couple, but the over-discharge protection limits the number of lights they are viable in).
Just my experience and opinion. Good to see you doing the legwork before jumping in. Best of luck…and P.S; buy yourself a cheap DMM to check your cell voltages if you don’t already have one.

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Heh-heh. Yoni…

Pffft…LOL. I was wondering what the giggity was. Had to look it up…I’ll edit my spelling.

Nice :+1:

What light, what batteries?

Probably a bit of a crapshoot, there will be enough variability in component electrical values that you could get one that charges to 4.15 or one that charges to 4.25V. Best to use a multimeter to measure yours and see for yourself.

Charger recommendation worth a separate thread, but think about power input (usb or mains or a separate PSU), number of slots, size of slots, charge current options, analyser options.

Small overcharge 4.25V will shorten the life of the cells, large overcharge (4.25+V) can result in fire.

Some lights physically need a button/nipple to reach the contact, others have a longer post or spring on the + contact so can use flat tops. Protected cells are good when you’re using more than one in series, or if you have a light without low voltage protection (3V is pretty much empty for lithium ion, and shouldn’t be drained any further).

Convenience Vs another failure point, and will likely be longer than regular 18650 cells so might not fit all lights. Personally I avoid.

Brand and reliable seller. I only buy cells from a highly rated UK seller, I got a bunch of mystery 18650 cells from china a few years ago and am a bit nervous of using them as they’re definitely not real Samsung 30Q’s.

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Thanks, I chose a little more neutral emitter for color rendering. Hoping I like it. Also not sure what to expect for battery life and output, as the only specs on the light are % outputs with no indication of battery life. I’ll need to play around with it and get a sense for it.

Well, I have 4 lights currently that cover everything for me, and I guess all of them have the ability to use rechargeable cells. My daily carry is a Lumintop Tool AA 2.0 and I got a Lumintop 920 mAh 14500 with it, which charges via USB-C port in the cell. Then I have a Trunite W1 that came with a Thrunite 16340 and the light charges via micro USB onboard charging. My headlamp for the last several years has been the Fenix HM50R, which also has a Fenix 16340 with onboard charging through a micro USB port on the light. Lastly, I have a Thrunite Archer Mini which has USB-C onboard charging and runs off of an integrated cell that cannot be removed (which I do not like and will not purchase another light that has to be discarded when the cell dies, but it was relatively inexpensive and I like the other feature).

I didn’t have to make my own battery choice for any of those, since all of them at least had the option to come with a battery branded to match the flashlight. And I didn’t have to choose a charger, as they can all charge simply using cables I already have around. I will say that I prefer to NOT have onboard charging on the flashlight if possible. The port and rubber cover just seem like an extra failure point on the light. I prefer, like the Tool AA, to be able to use either a Li-ion rechargeable cell (that I remove to charge) or a standard disposable cell from the grocery store in a pinch. My headlamp can also use a CR123A and I think the W1 might be able to do so as well, though I haven’t tested it.

That’s easy enough. Just hold a probe against both battery terminals before and after charging?

Charge current options are the thing I am most curious but most ignorant about. I’m guessing higher currents charge faster but decrease cell life over time?

That’s exactly the kind of info I needed to know. Thanks.

Thanks. I’ll keep that in mind. I don’t think I’ve ever noticed “low voltage protection” in a spec sheet. Is there a way to find that out?

Makes total sense. My Lumintop 14500 cells with a USB-C port in the cell fit obviously fit just fine in my Lumintop flashlight, but I guess I shouldn’t assume a fit in other lights.

So most decent cells are just re-wrapped Samsung 30Q cells? And recognizable brands and reliable sellers should be using those?

Yes that’s a commonly discussed trade-off against rubber cover onboard charging.

The voltage of the cell will “relax” after removing it from the charger, if you have a convenient shaped charger or very narrow DMM probes, you can measure the “live” voltage directly from the contacts while the cell is charging. Else, you can put a small piece of conductive metal between the cell and the charger contacts, for you to reach them with the DMM.

Normally companies advertise whether lights have LVP, Low Voltage Protection, or Low Voltage Shutoff. There’s a bunch of different behaviours (hard shutoff, graceful decline, flashing, etc). Good reviews should measure/test the low voltage protection and behaviour.

As an FYI, most cell manufacturers are quite clear that the way we use “naked” cells is forbidden.

I avoid rewraps as I like to know what the original cell is. 30Q is a pretty okay cell, capacity and current do everything I want in my lights.

Most important is to use a reliable seller. There’s a thread somewhere on here about “where to get cells anywhere in the world”.

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Thanks for all the info. I really appreciate it.

I’m headed to buy a DMM (used them occasionally in the past, but never bought my own to keep at my bench). I wanted to clarify a couple of things: Will an overcharged battery “relax” a normal voltage and make it difficult to detect that it has been overcharged? Are you saying that, to determine if a charger has overcharged the battery, I need to test it before removing from the charger?

I just assumed that after charging and removing from the charger, I could check the battery with the DMM to see if if exceeded the max voltage of 4.2V. But if that’s not sufficient, then I’m all ears.

Most flashlight sellers will specify in the description of the light you are buying which battery type works for the light. If not listed, find a version of the light that comes with a battery and see what type of battery they are using (button top vs flat top vs usbc battery etc). I have several convoy lights and my experience with the LiitoKala batteries has been that they are fantastic and reliable.

My main concern from your post is the charger you are using. Honestly I feel as though the only chargers that should be sold are the bay chargers with overcharge protection. You are going to want to get a nicer charger than the one you described. You can look up best chargers for lithium ion batteries and pick what you like, but as a general rule look for the ones that fit a wide range of battery sizes (18350-21700-26650 etc). Also make sure the charger has a little indicator display that shows the charging status of the battery. The good chargers will show you a percentage, most chargers have four status indicators to show 25%, 50%, 75%, 100% capacity. Convoy sells a good LiitoKala bay charger that meets this description and is under $10. It will not overcharge your batteries but as a general safety rule don’t charge overnight or leave batteries unattended while charging. I charge mine on a little stand next to my tv or my computer desk while I am browsing.

You can also look up general tips for using li-ion batteries, but the biggest tip for longevity would be not to store them at 100% or below 30%. I keep mine around 80% when not using them and will top them off before I use them if I plan on needing them for something specific. You also don’t want to let them get too low in voltage. I will do a charge status check occasionally by popping the battery into my charging bay just to see what % charged the battery is.

It sounds like a lot but once you get the basics of how to properly use them, these batteries are actually super low maintenance and should give you great performance for many years.

If the charger has recently indicated “full”, pulling the cell and measuring voltage will probably be fine to tell you if it’s over charging.

Measuring while cell in charger can confirm that the charger shuts down when cell is full (it’s very bad practice to continue to trickle charge Lithium ions).

FYI there is similar behaviour at empty- a cell under load will be lower voltage than one that’s “rebounded” slightly after removing it from a device.

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