BATTERIES - Selecting the Proper Battery for your 365nm UV Flashlight, Convoy S2, Convoy C8, FyrFly


This GlowNotes post is compiled from a post in our Fluorescent Mineral Facebook Group. Several folks added some great information about a frequently recurring question to a PSA battery post I made. Archived here for future reference.

Be very careful - there's a lot of junk coming from China, much of it counterfeit, much of it fake. 18650 and CR123 batteries are a ripe area for this fakery. One company in our hobby is (was, I hope) selling yellow Etsair 9900mah batteries) along with a new light they area selling. This battery is not only fake, it's outright dangerous. Available on Ebay for $2/ea (much less in quantity) the specs are an outright lie; 9900mah is a ridiculous claim. These types of batteries can overdischarge, overheat, and burn. I would NEVER bring this battery on a plane. Lots of websites will help you spot a fake:


Buy only from trusted dealers and manufacturers. Midnight Minerals and Engenious Designs both sell batteries for their lights, and are very knowledgeable in the area. Be very wary of batteries on Ebay, batteries over 3500mah, and cheap prices. Panasonic, Orbtronic, Sanyo, EBL, are some of the trusted brands.

A quote from EEVblog Electronics Community Forum:

"In general, the Ah capacity of batteries sold from China are not worth the plastic they are printed on. The vendors/manufacturers lie so they can get you to click on buying theirs over some other fraudster's batteries. Best to buy genuine Sanyo Eneloop or genuine Panasonics. Problem is the Chinese are so good at pirating the genuine article you cannot tell the difference from the outside. This is particularly the case with mobile and cordless phone replacement batteries. There are many "Genuine" Samsung batteries (complete with barcode or hologram) that are just fakes, imported from China and sold locally via eBay. If you want to eliminate the risk, buy from a reputable dealer in your country, not from eBay. Most of the torches sold on eBay from China are also rubbish. They don't last very long. Best to pay more for a reputable brand from a reputable retailer. Years ago retail stores sold boom boxes (AM/FM cassette stereos you carted on your shoulder) that boasted "20,000 mW of Peak Power!". One I saw stated something like "1,000,000 uW power output" on a cheap no-name cassette stereo! They were marketing to the ignorant masses. The manufacturers did not lie, just exploited non-technical people by making the numbers look good. With the 9900 mAh batteries they not only marketing to the ignorant masses, they are straight out lying. In the end you get what you pay for."

Members of our group posted recommendations based on their experience. These can be a great starting point in selecting a good battery for your flashlight. Be very aware that name brand batteries are often counterfeits - the best protection is buying from a reputable vendor. Ebay is NOT a reputable vendor. There are of course many reputable sellers on Ebay - just make sure you know who they are.

Much of the discussion below is centered around 18650 batteries, but they all also apply to the shorter RCR123 batteries (rechargeable CR123's) which are used in the Convoy C8 FyrFly (my preferred size - I just like a short flashlight). Two sections archive the general information posts, with specific battery recommnedations below that

General Information (poster names removed, no particular order)

  • So what's the moral of this story? Frankly, you can take the capacity ratings on the cells with a grain of salt. As a matter of fact, some of the good cells label their part numbers and other data and don't put mAh capacity ratings on them. They know how to print the fakes ones the same way. Put a cell on a scale. "Generally", I find the weight of the cell is proportional to the measured specs I get on cells I look at. Your good name brands are going to be on the heavier side, the mid-grade "fakes" are going to be in the middle and the real junk cells are usually lighter. Just an observation. So I would say there are sort of three classes of these cells. Ones that are downright underpowered and dangerous, there are some mid-grade average cells with labels that are all lies, then higher performers with higher capacities and some with or without protection. I don't run a battery test lab by any means. But I do check everything I receive in to ensure reliability as I receive it. If the battery is feather light and it heats up on a charger like a bagel in a toaster, DON'T RUN IT IN A UV FLASHLIGHT!!!!! And don't charge it again! Properly discard it!

  • There's a guy that does battery testing that i always check before buying a new cell.

  • There is no such thing as a 9800mah 18650 battery. At best, your batteries are just lies. At worst they can explode if shorted out, or improperly charged/discharged How long they will last depends on what kind of Convoy you have (the first version draws under 700ma and will last the longest). But "last" doesn't mean the light is putting out full brightness. As the battery discharges it will get dimmer. I would not use the battery you show - clearly fake, so who knows what else is inside.

  • Legitimate battery companies wouldn't market the mAh value on their battery in such big numbers

  • Reputable brands are all made in China but some have their own quality assurance people working at the production facilities some do not. Some of the products made for the various reputable brands are rejected by the QA and then sold as no name brands.

  • Ebay doesn't give a hoot about counterfeits. Years ago an SD card failed & I determined it was counterfeit. Ebay's response was just that it was past their deadline for disputing & let the seller keep on selling his trash.

  • I guess number one thing is I have never heard of anybody using a UV flashlight and catching any batteries on fire. This is a way different use than that of those vape devices which get modded to make bigger and bigger clouds. Way less current used than that application. I also think our normal hobby user is smart enough not to throw a spare 18650 into a pocket with a bunch of loose change.

One observation that can be made on most any cell that will not take any special electronic testing equipment or technical background is to weigh a cell. On average I see most of the good cells are 44 grams and heavier. So when buying cells, if they don't divulge weight, I would not buy them. The cells I have seen that are the lowest capacity I have ever seen weighed in at 25 grams. There is certainly a correlation to weight and capacity. There is a practice where small form-factor cells/packs are embedded in an 18650 package and soldered in - sometimes with some filler in there to take up the extra space. Fakes!

Mark's note on BatteryUniversity is one I have looked at before. That is a great place to gather lots of info.

Highest capacity cell I have ever tested was an Orbtronics ORB3500P cell. It measured 3248 mAh actual capacity. I think due to the protection circuit, it measured at 190 miliohms. My observation is protected cells measure out with higher IR.

The Samsung ICR18650-25R cells I generally like to work with have a fairly consistent IR in the 30's and capacity holds pretty true to the 2500 mAh rating - some under some over.

Lowest capacity cells I have measured were these purple cells called IMR18650 Li-MN. Those feather light batteries only have 485 mAh capacity and average 95 miliohms IR. Although many eBay batteries are JUNK, these are REALLY JUNK. At least some of the eBay batteries that claim 9900 or 12000 mAh will actually deliver around 1000 mAh. And will do so fairly consistently. So junk. But consistent. :)

I have checked out various cell manufacturers. EBL, ETSAIR, Fenix, Garberiel, GTL, LG, Nuon, Orbtronics, Panasonic, Samsung, Sofirn, Sony, Trustfire and Ultrafire. Everybody has their favorites. If you find the capacity and consistency with any of the cells you have experience with, you should stay with your brand loyalty. Always keep an open mind about other makers though. I have personally had great results with a specific Samsung cell. But I try to keep that open mind and watch some of the technology trends.

  • and has some good info.



Specific Batteries - Member Recommendations/Warnings: (poster names removed, no particular order)

  • Have had good luck with the Panasonic

  • If you're looking for NiMh batteries, the Panasonic Eneloop is considered the best in the market. Get them, you won't be disappointed. Do your research about lithium batteries, the different chemistries, and know what kind of amperage your device needs. Unless you really need an unprotected battery, I recommend always buying lithium batteries that have an integrated protection circuit. There are other good retailers, but I but my eneloops and 18650's from Great company!

  • I have had great success with batteries from NiteCore. They seem to be true to their capacity, but even better is that they offer models with built-in microUSB charging ports so there is no need for a separate charger, just a free USB port on your computer or a phone charger (though the microUSB cables are sold separately).

  • I have bought many of these and can attest that they are amazing: They also have 8A 18650 batteries, which is something to consider. While listed at 3500mAh, these batteries when loaded into a Convoy S2+ appear to notably brighten the output:

  • My favorite, reliable battery on single-cell convoys has been the Samsung 18650-25R's. Mostly since they are all pretty reliably close to the 2500 mAh capacity. Nice low internal resistance and quite frankly they fit in the Convoys nice being the flat top style. Obviously the 2x cell version (for the Convoy C8, 18650 version) cannot use this type, a button-top version is needed.

  • I know folks have discussed the cheap-chinese-fake cells. I have certainly found some that were terrible. I found the ones I got from Ultrafire to be the worst. But I never tried that brand in the yellow wrap.

  • Frankly, I have heard a lot of folks with the yellow Ultrafires are pretty happy with them. So for those of you that love them, I'm basically still not going to go down that road. The only battery with the name FIRE in it that I have found to be pretty OK was TrustFire. And actually so far UniqueFire didn't seem like a dud either. Uniquefires had 2200-2300 mAh actual capacity. TrustFires had 2500-2800 mAh actual. But you can tell TrustFire has that same low internal resistance as the Samsungs. Where the Uniquefires are in the 150 mOhm range. Where UltraFires I have looked at were up over 300. I generally find the cells that are above average with electrical validation, generally hold up well on the scale. 45+ grams. Orbtronics are like 48+ grams. UniqueFire and TrustFire are over 45 as well. Sony, Panasonic, LG, Fenix, Where the ultrafires I checked were probably ballasted up to be 42g.

  • EBLs that I have tried come in a little under 45g and have IR at around 100 mOhms. But they seem OK. Then I have cells that have actually delivered quite reliably, never get hot on charger and have been an OK economy cell. Once again by weight, they seem to fall into a class of cell that is right around 36 grams.

  • The yellow ETSAIR cells have a realistic capacity of 1000 mAh out of the 9900 on the label. But I have never, ever had any issues.

  • Garberiel cells have a slight bump and deliver around 1200-1300 mAh out of the 6000 on their label. Once again a downright lie. But, for the economy cells, these have been pretty descent for me. Rather low IR too down toward 60. Not as low as Samsung 25R's which are like 30-40. But pretty low considering Garberiel is in what we are considering the Chinese junk right? But you get about 4.8 Wh out of the dang things.

  • I would say the worst performing cell I have seen were the blue Ultrafires I have checked. They just heat right up in your charger. No way I would recommend the specific ones I have anyway.

  • But there is a cell that charges OK and have that medium IR measurement. But they have only like 475 mAh capacity out of the 2500 they are labeled. It is these purple IMR18650 cells. They ONLY weigh 25 grams max. They even sound hollow if you clink two cells together. Never heard a sound quite like it.

  • Orbtronic 3500mah High Drain 18650 batteries were recommended to me. Anybody else use

  • I have a 1/2 dozen I rotate through the devices.

  • I use ultra fire 6000mAh 4.2 V. Li-ion. Red

  • They sure do make the best fires ;-)

  • I bought two ultrafires once to test and evaluate. They arrived at the door basically dead. One was like 0.9 volts. Other was 2.6 or something. Attempted to put a charge to them outside. They heated up pretty quick at 1A rate. I attempted something like 100ma rate later to see if I could coax something into them. The really, really dead one wouldn't charge. The other one, I got to go to 4.2 v sort of. Once the cycle ended, the actual voltage of cell was only like 3.2. This one that sort of charged had something like a 600-700 mΩ internal resistance. WAY, WAY, over normal. :) So, I'm assuming you're joking about Ultrafire cells being your goto

  • I have been using them for the last 4yrs and haven’t had any problems. I just got 4 new ones they charged up with no problem will let you know what happens

  • That sounds great! I have heard less than stellar reviews of Ultrafire right here in this group. Sure enough, the one I bought was total junk. It was sort of like someone telling me "whatever you do, don't push that red button". :) What did I do, went out and bought a couple. Luckily no ultra fires erupted. But mine were DOA and I simply got my money back from the seller. So all ended well.

  • I have a couple of Ultrafire 18650 batteries that came with my original long wave LED lights 7-8 years ago. They work, but their capacity is about 1/5 the stated value printed on the battery. You can measure them on a scale - they are way lighter than "good" 18650 batteries.

  • Samsung, Sanyo, Panasonic are all supposed to be good. I tend to buy more expensive batteries on the theory that they are less likely to be fakes. An easy way to tell is weight. The fakes are usually less than 45g, usually a LOT less

  • I'm getting more mAh. I have an Ultrafire branded battery that came with an older light I have. I think it says 2500 mAh. It actually has about 500. That is true for many batteries. Also, I want protection circuitry that is likely to work.

  • I chose to buy from Orbtronic directly- I got questions answered and recommendations from them that I'm unlikely to have gotten from an eBay seller, and would definitely buy from them again, even if the price is a little higher. To me, the customer service and peace of mind is well worth paying a couple dollars more.

Leave a comment

Please note: comments must be approved before they are published.

.ezsd-arrows .ezsd-arrows_arrow { position: relative !important; padding: 0; height: 100%; pointer-events: all; opacity: 0.9; background-color: white !important; }