Well, what you’re asking is to tell you if you can take
— two cells that you get from somewhere
— some circuit board for IC protection that you get somewhere
— some solder to stick them together
— a charger you trust with your life but don’t have any test info on
and put them all together safely and plug it all in and be safe.
I think the only answer you can get here from anyone with experience buying components is:
“Do ya feel lucky? Well, do ya?”
Nobody can tell you for sure that any component you buy is as described.
People lie about selling crap. Trust your source because you know they test what they sell you.
Don't get me wrong here Hank. But imho this things should not be rocket science and we should not make rocket science out of that.
If we have "recipe" to make our own flashlights, drivers and improve flashlights to be superior in performance to factory one why we should afraid to build mentioned battery pack :) ? Should we be scared when we do mod of our first flashlight? Answer is probably yes but the point of this forum is to learn people do things by themselves and that happens when just few talented members share their knowledge. To learn something from some person that can be on the other part of the world is really great experience.
So as it really is as it looks with Eagletac battery (2 x protected 18650 batteries connected with magnet and re-wrapped) That mod could do 12 year old kid.
Selfbuilt. Great reviewer from CPF did review of Eagtec series flashlight, charger, and battery pack here
I would quote his opinion on Eagtack battery pack:
"The GX25L2 uses a 2x18650 battery pack – shown here as a single shrink-wrapped package. Based on the label, it looks like they just using two button-top Eagletac 3100mAh protected 18650 cells wrapped together in series.
You can thus use your own cells easily enough, but as will all multi-cell setups, you should make sure to only use well-matched cells (i.e., same brand and batch, similar history of use, consistent charge, etc.). Use of a pre-supplied battery pack takes the guess work out of this.
Note the charger will work with your own cells as well – but again, particular care should be taken when charging cells in series (i.e., important they both be at a comparable charge state, with well-matched characteristics)."
His reviewed chargers also looks like generic type non balancing charger?
So why to pay 40$ with shipping for battery pack(eagtac type) if I can make 10$ free shipping one?
Most of us here are probably to occupied with flashlight modding.
Modding battery or making battery packs is taboo here? We will see... Time will show. Some member will rise up and learn us how to properly do that without fear of burn something out :)
Its not really taboo, its the safety implications and the result if something goes wrong. If someone has given advise and something does go wrong, they will live with those consequences as well.
People probably have done what you are asking but are only willing to take on that risk themselves. Its for the same reason that the blf a6 had a timed stepdown. We all know not to tailstand on max but when its sold outside of blf, anyone could get their hands on it.
Should be more than $10 for a good pair of seiko protected batteries.
Nothing too taboo or difficult about the pack itself but the whole of what you’re looking to do should only be done by someone who is careful and understands, appreciates the risks. The fact that you’re not even willing to entertain the possibility that the 8.4v charger which you linked to could be unsafe does not really point toward you being that careful or open, to be quite honest. Right on the page you linked, the seller doesn’t even try to claim it a proper cc/cv li-ion charger.
Just series battery pack. Batteries are brand cells protected LG18650D1 from this seller. So they are 10,50 per 2 pcs via Sweden post. Not a single failure on them so far. I charge them with 4,2 charger although they are 4,35V cells so they should last.
When we build flashlight all kind of dangerous nasty stuff can happen and we are more or less aware of that, and of course it will be our risk no matter lets say Djozz explained well that in his thread.
It’s just not clear what you’re asking us to help you do.
This is not the place to get quality assurance information you can use to reassure other people.
This is a gambling place for people willing to knowingly take chances.
I don’t understand why the cells need to be fixed together? ALL of the problems that everyone has been pointing out to you would be non issues and you could charge them in a regular 2 cell charger. [edit] well except for uneven discharge, but you would see the problem the next time you charged.[/edit]
I have a couple Home Depot Defiant brand 2x AA lights that the cells rattle in. I cut a sheet of notebook paper to the right size and made a sleeve that the cells fit in. Stopped the rattle, but easy to slide them in and out.
I want that someone with experience in building battery packs show us how to safely made series battery pack. It can be in Eaglatack straight style or parallel. And maybe to show us charger he uses. We are taking responsibility for eventually bad assembling or any other dangerous situation.
No I would not resell them. Just for my personal use.
In all situations where battery needs to be lets say permanently fixed over, under or inside something and you don't want a hassle of dissembling and charging cell by cell and where you want plug and play action.
We all know what you mentioned. It is no problem to take side by side series box(1-2$ costs) and to make cradle. Although I did not seen series tube? Series tube could be useful and battery could be replaced faster and it would be thinner and more practical for certain situations but it does not exists. I don't see any issues can happen with this method cause we use regular chargers on that. But then If you have something that you need to unscrew (like lets say 5-10 screws to get under the hood and remove battery by battery and manually charge it and then return back to cradle is not practical at all :) you would say f... that I want battery pack and charge it on the hood :) ).
So as I said to Hank:
I want that someone with experience in building battery packs show us how to safely made our own series battery pack. It can be in Eaglatack straight style or side by side. And maybe to show us charger he uses. We are taking responsibility for eventually bad assembling or any other dangerous situation same like for any kind of flashlight build.
We are all Borg on BLF when it comes to flashlight modding :)
I got to have fixed 18650 battery pack(preferable in eagtac style) with soldered dc male/female jack.
I would use them for my camera system. But I could use them in flashlights in future. Why not? :)
Hobby charger is something that I can afford but I like to make things simple. If there is any kind of small charger that could charge that pack that would be better solution. Maybe my 8.4V would charge them good since it already charged plenty of small phone cells 8,4V battery packs. Who knows?
I am just worried about safety of this, and when I am not sure I don't even wont to try.
But on BLF I still did not find thread how to safely build fixed series battery pack cause we all use classic 18650 chargers.
Edit: I had series flashlight in past like DBS with buck driver but I am mostly building 1x18650 lights.
I’ve taken apart some 2 cell series battery manufactured as a stick. First was a Cabelas XPG X-TREME LI, it charged in isolated series and discharged in non isolated series. The other was a bike light it charged in parallel and discharged in series. When I took the packs apart they had pretty good pcb’s clearly showing input and output leads from the pcb. It’s not to hard with good pcb’s to charge one way and discharge another, diodes aren’t always in the front of the light. This is how multi cell packs are charged and discharged, like power tools and laptop batteries.
Now as to how the original poster presented his method, I would say no. On your described method they would charge until one pcb detected over voltage caused by the other cell not charging as fast. This would intern slowly cause the cells to further go unbalanced as one worked and charged harder than the other. Pcb’s on single cells aren’t wired to monitor the other cell. This isn’t dangerous but just not as efficient as separate charging.
I want that someone with experience in building battery packs show us how to safely made our own series battery pack. It can be in Eaglatack straight style or side by side. And maybe to show us charger he uses. We are taking responsibility for eventually bad assembling or any other dangerous situation same like for any kind of flashlight build. ”
First folks have been giving valid advice, whether that rises to the level of “safely” is up to you.
To review
A) keep the cells separate, thus charging and monitoring can be done individually.
B) Use a balance charger. (because over time the cells will not stay perfectly identical no matter what)
C) If not using a balance charger then at least “Bottom Balance” the cells before joining them. (it is more important that both cells run down to the same near exact voltage as opposed to being topped off to the near exact voltage) all the caveats of using identical cells are still valid. (having the protection circuits on each cell may limit the voltage one can balance them at, (but something is better then nothing)
Building a safe battery pack is a separate issue from how it is charged. Two cells in series is no big deal. The ability to separately monitor and charge them is important. (A] use cells separately and charge and monitor separately, B] use a balance charge to monitor and charge separately)
If using “good” identical cells and if you do not monitor separately then all that will happen (probably) is to loose some capacity over time.
If using “poor” identical cells and if you do not monitor separately then it is more probable that “large” charge differences can happen over time. What are the risks of “large” charge differences? I think we all know in principal.
“Hold 2 piece 18650 batteries
Keep your battery organized and protected
Specially designed with modern build-in protection circuit module
It’s flexible and convenient for various customized application
Maximal continuous Charging current 5A
Maximal continuous Discharging current 5A
*Over charge detection voltage 4.25±0.025V
Over discharge detection voltage 2.40±0.08V*
Over current detection current 6.5±1A”
Now I don’t understand how a “Over charge detection voltage 4.25±0.025V”
works in a 2S battery pack.
The spec to me says 2P
but maybe they just got the details wrong (is this really the charger you want) and besides how are you going to fit that long permanent s2 battery in there?
If you are not going to make them permanent 2s then you are just like the rest of us and go and get a decent 18650 charger.
Or maybe I just don’t get the project, which is ok also.
They are generally the sort of thing I could use. I want to build a couple of packs of about 12V with 3 or 4 parallel cells (9 or 12 cells).
I am not seeing coherent specs for protection circuits.
Some are listed with Over charge detection voltage4.325±0.025V - that does not seem like a good thing unless you have some high voltage cells.
Specs show protection for 1 cell voltage in a series pack of n (e.g., 3). Implies protection per cell if the number is right for the "pack".Or that you take the cells out to charge.
No information on how one charges the things. The wires look kind of thin.
It could just be very sloppy writing for the specs. But they show these things have been around for a bunch of years and one would think they would have straightened it out by now.
explained well that in his thread. 
