# How to disassemble a Li-Ion pack



## EvilLithiumMan (Dec 3, 2003)

(Use the following information at your own risk. It is a documentation of my own experience that others may find useful)

I'm no authority on the subject, but I have disassembled about 10 Lithium-Ion packs for the express purpose of making my own for use in flashlights. The goal here is to take apart a Li-Ion pack, including the protection circuit board (PCB), without destroying anything or burning down your home. It can be done by working slowly and understanding every step.

Li-Ion packs consist of two parts, the base and the cover, which are electrosonically welded together. (I assume that's how they are joined, as I have yet to find any evidence of an adhesive). This bond is not particularly tough, but care must taken to avoid shorting the cells when cutting into the pack.

This procedure will use a Canon BP-511 as the example. It contains two 18500 cells which, when arranged end-to-end, are only 3 millimeters longer than two C cells. Makes an ideal pack for the Maglite 2C and saves on CR123 costs.

For purposes of this discussion, I define the 'front' of the pack as that end which has the protection circuit and electrical contacts to the base.

Here is a BP-511, standing on its end, so the 'front' of the pack is at the top in this view:






Make the first cut at one of the 'back' corners of the pack. Use an Exacto knife and go in at a 45 degree angle. (Exercise great care when using an Exacto knife. I know I do). Rock the blade back and forth and cut into the corner. You will hear a snap or a crack when the seam breaks, which is just what you want. It signifies you have started to seperate the cover from the base.

Start by cutting into both 'back' corners:





When finished with the 'back' corners, do the same at the 'front' corners. Do not do any other cutting at the front, as the protection circuit is directly behind the cover. Once the corners are complete, go again to the back and run your knife along the rear seam. This will take many passes, but eventually you will hear more cracking as the seam separates. (Again, be careful with your knife)

Now the sides seams need to be cut, using the same slow, deliberate technique. The cells are directly against the side seams, so your knife will probably cut through the cell's vinyl insulation, but nothing will be shorted.

With the back and side seams cut, the pack should look like this:





If you've got this far without severing an artery, my bandaged hand salutes you! What needs to be done now is to lift the cover off the cells, just as if you were to open the hood of an automoble. But there is a problem - all of the packs I have worked with so far have the cover stuck to the cells with an adhesive. Pulling the cover up with the cells attached will break the protection circuit board, which is firmly attached to the base.

Disaster awaits - the cells are coming up with the cover:





We need the cells to remain seated in the base, while only the cover itself swings up. Use a small screwdriver to pry the cover away from the cells.

Note! - Pry against the negative cell only!:





If you pry against the positive cell and the screwdriver cuts through that cell's insulation, you will know it right away, you're shorting it out! (If you don't understand this and the preceeding image, stop until you do. There are two cells, but only one is acceptable for prying up the cover).

O.K. - the 'hood' (cover) is popped and the cells remain seated in the base:





Remove the cover and discard it. The next step is to desolder the protection circuit board (PCB) from the base.
Before we do that, we need to know what connections are on the PCB and the best order in which to desolder them. Of the three different types of packs I have worked with, they all used the same designators:

'B+' This is the battery's physical and electrical positive connection.

'B-' This is the battery's physical and electrical negative connection.

'V+' This is the positive output of the battery pack. (Note the distinction between the 'battery' itself (B+,B-) and the 'battery pack' (V+,V-))

'V-' This is the negative output of the battery pack.

'D1 or D' One side of the temperature sensing diode.

'D2 or B' Remaining side of the temperature sensing diode.

'BM' For two cells packs (7.2v), this would be the 'center tap' of the two batteries. I'm guessing 'BM' stands for 'Battery Match'. If one cell was 4.6 volts and the other cell was 2.6 volts, total battery voltage would be the correct value of 7.2 volts. But obviously, one cell is in danger of being overcharged while the other is serverely discharged. The protection circuit monitors that both cells are close to the same voltage; if not it will turn off the pack. 3.6 volt packs have only one cell, so this connection does not exist for them.

Some more notes:
'B+' and 'V+' are electrically connected together; one and the same. The n-channel FET protection circuit exists only in the negative side of the battery pack. This agrees with every design note I have read regarding Li-Ion protection circuits.

Although all of the two cell packs (7.2v) I have seen have temperature sensing diode connections, I have never seen them utilized in a battery charger. I have four after market Li-Ion battery chargers. They all have only two terminals, '+' and '-'.

O.K. - refer to this photo for the connections on the PCB:





Starting on the left, we see the 'B-' connection. The two pads that follow are for the temperature sensing diode. In the middle of the PCB we see the 'BM' (center tap) pad with the strap connected to it. Just below and to the right of the 'BM' pad is the 'V-' pad. (You can't see the marking from this view). On the far right is the 'B+' pad. And just below the 'B+' pad is the 'V+' pad.

The first connection to desolder is the easiest, the 'BM' pad, right in the middle of the PCB. There is a piece of tape covering the strap. Remove the tape and put a fingernail underneath the strap and exert a mild upward pressure. The strap will pop up when the pad is heated; it will only take a second. Lift the strap straight up so it is temporarily out of the way.

Now lift the battery pack up at the rear so it just clears the base and pull back on it slightly. Desolder the two diode pads. They should pop away from the board when heated, due to the mild force of pulling back on the cells.

Diode pads and the center 'BM' pad are now cleared:





With those pads cleared, we can now pull back even more on the cells and desolder the 'V-' and 'V+' pads.

Cells and PCB are now separated from the base:





The only connections remaining are 'B-' and 'B+'. They are wrapped around each side of the PCB:





Put a little pressure on the cells with your fingers. As soon as you hit 'B-' or 'B+' with the solder iron, it will come right apart:





It's all done. A Li-Ion battery pack with protection circuit can now be reassembled in a form factor to one's liking:





I now have a Mag 2C that not only uses CR123 cells, but also has a Li-Ion pack which can be recharged many times.

Some final notes:
When assembling a battery pack, don't rely simply on the cells existing vinyl insulation, it's not very tough. Case in point - placing the two example cells in series looks safe, but the second cell's connection on it's positive terminal overlaps and touches the vinyl insulation of the cell. The Maglite seems to exert a lot of pressure on the cells, so I added some high strength dielectric tape to the assembly.

Added insulation: 





When connecting up the PCB (protection circuit board), 'B-' will go directly to the cells negative terminal. You then must cover this with an insulator and add a second electrode which will be connected to 'V-' of the PCB. If you fail to do this, you won't have any protection against excessive discharge or overvoltage when charging. Finally, make sure you leave enough of the 'V+' and 'V-' connections exposed so you can connect alligator or mini-hook leads to the battery pack. You can then recharge by connecting the leads to any functional Li-Ion charger.

FINI


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## Mark_Larson (Dec 3, 2003)

Very well done. An excellent write-up!

Maybe you could post some sources of the batteries and the packs? (As in the packs themselves and places to buy them at)

Once again, excellent writeup. :thubsup:


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## nexro (Dec 3, 2003)

thanks for the useful information!
I have always thought of doing something like this.
However, I don't have any Lithium packs to spare... I do have some NiMH battery pack lying around. Might try it on them /ubbthreads/images/graemlins/smile.gif
One question though, will mis-handling these lithium batteries/NiMH batteries cause them to explode?


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## PaulW (Dec 3, 2003)

ELM,

. . . a beautifully composed tutorial. It's not only informative, but a captivating read. Although I don't "need" this information at the moment, I may someday, and your write-up has certainly improved my understanding of how protection circuitry works and what's protected -- a valuable concept.

Many thanks for your outstanding work. /ubbthreads/images/graemlins/thumbsup.gif

Paul


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## EvilLithiumMan (Dec 3, 2003)

Mark, thanks for the kind words. As for the Li-Ion packs, I buy them on eBay. There are lots of sellers and pricing is competitive. Three years ago a spare pack for my Powershot G2 was $35; today they are under $10.

Here's a list of what to search for and what it contains:

NP-80 3.6v, 18500 cell
NP-100 3.6v, 18650 cell
BP-511 7.2v, two 18500 cells
BN-V812 7.2v, two 18650 cells
BP-945 7.2v, six 18650 cells

The BP-945 I haven't disassembled as I am using it as a direct replacement for a 6 volt lantern battery:





It provides nine hours of run time using a KPR118 bulb. It contains three pair of 18650 cells in parallel and may not be so easy to open - I just don't have the need to try at the moment.

nexro, Li-Ion cells can be a literal blast if handled improperly. Always use a charger designed for them; never try to charge them with a Nicad charger. Do a search in this forum for 'Li-Ion FAQ safety'. You will find a great FAQ by koala on Li-Ion characteristics.

ELM knows no bounds - bought this charger for my 3.6v NP-80 cells:





When I removed the adapter plate I found three contacts:





Why three contacts when only two are needed? It turns out the charger will also handle 7.2v packs. So I ripped open the adapter plate and fitted it with a toggle switch. I can now select either 3.6v or 7.2v. Naturally the 7.2v packs don't physically fit the charger; clips leads and Solder Wick taped to the battery terminals work great though.

I'm so evil: /ubbthreads/images/graemlins/grin.gif


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## Mark_Paulus (Dec 3, 2003)

Very nice tutorial.

One thing I have found opening my IBM 600 Battery Packs. If I use a flat tip screwdriver, lay it flat on the pack so that the edge is parallel with the seam and right below the seam, I can push down until I hear the "crack" of the seam breaking. I then slide down a bit, and do it again. I generally do this on the long side, where I have more flex, and no circuitry. Keeps me from using a sharp blade and making everything bloody.


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## Mark_Paulus (Dec 3, 2003)

Do you have specs, or know of a page listing specs for other Canon packs, such as the NB-1L, NB-2L, and others that I see on Ebay?


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## BatteryCharger (Dec 3, 2003)

How big, exactly, are 18650 cells?


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## PaulW (Dec 3, 2003)

They're the same size as their designator, i.e. 18 mm diameter and 65 mm long (approx.).

Paul


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## vcal (Dec 3, 2003)

Lithium Man;

Which commercial battery packs (#s) would yield the AA sized Li-lons?
TIA


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## Mark_Paulus (Dec 9, 2003)

Is there a way to determine the "sizing" of the protection circuitry, or how does that work? Are the protection circuits sized based upon voltage, mah, or a combination of both? (Can I get any 2 cell prot circuit rated at 7.4V, and use it for a 4 cell (2 series - parallel) 17670 setup running @ 7.4V, but at higher mah?)

Thanks for any input.


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## EvilLithiumMan (Dec 9, 2003)

Mark,

The Li-Ion protection circuit has three basic functions:

Under voltage
Over voltage
Over current / Short circuit

There may also be an over temperature function, but on the two packs where I have seen it employed it was independant of the protection circuit.

Over voltage is typically 4.25v +/- .05 volts per cell for coke based electrodes and 4.35v +/- .05 volts per cell for graphite based electrodes. I haven't run into a coke based pack myself; graphite seems to be the norm these days.

Under voltage is usually 2.4v +/- .1v per cell for either system. 

And you are correct that the current limit protection will be based on the nominal capacity of the pack. The customer can specify a wide range of current limit from protection circuit supplier. My understanding is that 1 1/2 to 2 times the cells nominal capacity is what is usually specified.

I have also verified that via empirical testing - a 7.2v 1850mah pack would shut down when connected to a 2 Ohm load, but ran O.K. until complete discharge with a 3 Ohm load. I.E. - a 3.6 amp load was too much; a 2.4 amp load was not.

Because all of my Li-Ion applications are with incandescent bulbs whose worse case load is under 1 amp, I can use a protection circuit from anything that I have come across.

If you search on Google for 'Li-Ion protection circuit' you will find many manufacturers and their specifications. Here is a PDF sheet from one:
http://www.callistoelectronics.com/pdf/lpu410-a.pdf


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## Mark_Paulus (Jan 15, 2004)

Evil,

I followed most of your walk-thru, up until you got to the stuff about reassembling the cells for packs. It's the "final notes" section that has me confused.

Why are we worried about Positive node / insulation overlaps?


Re-wiring the PCB is confusing also. I understand Battery negative going to B-. But where do I connect the "second electrode"? Also to the cell negative terminal? Or to B-?

Actually, accoring to how this pack is used, could I find a carrier for this, and then do the following:
Dissamble the pack, leaving the strap between the series connected cells.
Straighten the cells out, and lengthen one end of the PCB connections, so it now is also between the Cell stick positive and negative as before.
Add leads to V+ and V- that go to "pack" end caps (end caps are insulated from internal pack and connected only to V+ & V-).
Shrink Wrap the whole thing and call it a "2 D stick"?
Does that seem like the proper idea?
(If I get some time, I may try to put up a Visio diagram of what I'm thinking to help clarify, in case this is too confusing.)


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## EvilLithiumMan (Jan 16, 2004)

[ QUOTE ]
*Mark_Paulus said:*
Evil,

I followed most of your walk-thru, up until you got to the stuff about reassembling the cells for packs. It's the "final notes" section that has me confused.

Why are we worried about Positive node / insulation overlaps?


Re-wiring the PCB is confusing also. I understand Battery negative going to B-. But where do I connect the "second electrode"? Also to the cell negative terminal? Or to B-?



[/ QUOTE ]






As for the 'second electrode', it will be the 'V-' terminal, as defined in the original post. 'B-' is the negative terminal of the *cell* . 'V-' is the negative terminal of the completed *battery pack* .

Just think of the protection circuit as a 'sentry' or 'security guard' that sits between 'B-' and 'V-'. If voltage and the current are accepable, the 'security guard' (protection circuit) will allow current to flow from 'B-' to 'V-' (the load).

Test the completed pack by discharging it and monitor the voltage between 'V+' and 'V-' with a voltmeter. The voltage should suddenly drop to 0 as it approaches 2.5 or 5 volts for one or two cells respectively.

Once again, please understand everything that is being done before attempting it. (Boy, I should talk. I was careless on the last pack I disassembled and shorted a cell. The interconneting battery strap lit up like a filament and melted apart before I could even react to the situation). /ubbthreads/images/graemlins/frown.gif


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## TheFire (Jan 16, 2004)

ELM,

I just used the info here to help guide me through the beginning stages of a battery repair for a friend. Thanks for the info, it was handy to have inside pics of the pack before I started. /ubbthreads/images/graemlins/smile.gif

Paul


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## PlayboyJoeShmoe (Jan 16, 2004)

What is the danger of over discharging Li-Ion batteries? I have two cells plain. I am extremely careful charging them, but once I notice the light get dimmer I am sure they are under... gotta check that!


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## Doug S (Jan 16, 2004)

[ QUOTE ]
*PlayboyJoeShmoe said:*
What is the danger of over discharging Li-Ion batteries? I have two cells plain. I am extremely careful charging them, but once I notice the light get dimmer I am sure they are under... gotta check that!



[/ QUOTE ]
Not known [to me anyway]to be a safety issue. It just damages the cell.


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## Mark_Paulus (Jan 16, 2004)

[ QUOTE ]
*PlayboyJoeShmoe said:*
What is the danger of over discharging Li-Ion batteries? I have two cells plain. I am extremely careful charging them, but once I notice the light get dimmer I am sure they are under... gotta check that!



[/ QUOTE ]

From what I've been reading, if you over-discharge the cells (go below 3.0V, or so), the anode or cathode (can't remember which) basically disolves away, and the cell is worthless. So, instead of getting your 500+ recharges, you get nothing more, from one careless discharge.


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## EvilLithiumMan (Jan 16, 2004)

[ QUOTE ]
*Mark_Paulus said:*
[ QUOTE ]
*PlayboyJoeShmoe said:*
What is the danger of over discharging Li-Ion batteries? I have two cells plain. I am extremely careful charging them, but once I notice the light get dimmer I am sure they are under... gotta check that!



[/ QUOTE ]

From what I've been reading, if you over-discharge the cells (go below 3.0V, or so), the anode or cathode (can't remember which) basically disolves away, and the cell is worthless. So, instead of getting your 500+ recharges, you get nothing more, from one careless discharge. 

[/ QUOTE ]

Well, I don't think it's quite that sensitive. I built an unprotected 3.7V 3700mah pack using two 18650 cells in parallel. In a sweepingly brilliant maneuver, I managed to fall asleep during the first discharge test. When I woke, the pack was at .57 volts. After letting the pack recover some on its own, followed by a very low constant current charge, I managed to bring the pack back to its nominal operating level.

Obviously, I have no idea how severely I've affected the total long term usefulness of the pack. But it has gone through three cycles now and doesn't seem to be any worse for the experience. (And yes, I've since installed a protection circuit). /ubbthreads/images/graemlins/blush.gif


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## PlayboyJoeShmoe (Jan 16, 2004)

Then I must not be discharging them as far as I feared. The light they are in is just as bright as it ever was.

As I charge them one at a time I check the voltage as it charges. I use a cut-off of 4.30V. This is with the charge going in. Once off the charger the cells fall to right around 4V within 10 minutes. Does this sound about right?


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## CM (Apr 1, 2004)

Just came upon this post from another thread linked to it. Gotta give it a bump. Great post Evil! /ubbthreads/images/graemlins/grin.gif


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## danielo_d (Apr 2, 2004)

I just posted this  thread before reading yours. Thanks for all the info. I better re-read your great info, ELM! Especially about the protection circuit! 
I've opened up two Sony FM50's which had the 18500's. Both cells seem good. Modded a 2C flashlight w/a Krypton bulb. Similar to your mod. It's great that it's rechargable!!! I'm using an Energizer ER-CH2 that only has two contacts. So, the charger itself is not protected? It relies on the pack circuitry? So, I guess it shuts off only when the total Volts of pack reaches a certain level. Is it safe to charge the bare cells?

The reason I'm confused [more than usual] is, the pcb was telling the charger that the pack is fully charged after a few min's. Then in the camcorder, it ran down after 15 mins. I replaced the pack. Disassy'd this one and the cells seemed good. I ran a bulb rated 4.5V .75A for about 1/2 hr on one cell. [actually each cell.] Then I recharged the cells and did the mod w/o the pcb. It runs fine, but I think the pcb protection circuit is malf. or something else... hmmmmm.

any ideas?

TIA. 

Danno


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## Wildcat (Apr 6, 2004)

what are the bench power supplies that yall use called. Can you set these to charge to a certain voltage and such? You say you set it to 4.3v

I am electronially challenged, so speak like your telling your 5 year old son what is /ubbthreads/images/graemlins/smile.gif

Thanks


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## Doug S (Apr 6, 2004)

[ QUOTE ]
*Wildcat said:*
I am electronially challenged, so speak like your telling your 5 year old son what is /ubbthreads/images/graemlins/smile.gif

Thanks 

[/ QUOTE ]
Don't touch that power supply or you'll get a spanking! 
Seriously, charging Li-ion cells from a power supply is not an activity for the electronically challenged.


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## Wildcat (Apr 6, 2004)

Okay then, let me ask this. I have a Pila charger on the way. Can I just cut the PCB and wires off these 18650 cells I got out of a Qualcomm 820 battery? Will they charge and use normal then?


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## Doug S (Apr 6, 2004)

[ QUOTE ]
*Wildcat said:*
Okay then, let me ask this. I have a Pila charger on the way. Can I just cut the PCB and wires off these 18650 cells I got out of a Qualcomm 820 battery? Will they charge and use normal then? 

[/ QUOTE ]
You *could* do it but it would be a bad idea. As I understand it, the Pila chargers put out too high of a voltage for charging a bare cell.


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## Wildcat (Apr 6, 2004)

How am I supposed to charge thses suckers. Is there a thread that shows how to assemble these two cells with the PCB for use in a light?


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## HarryN (Apr 7, 2004)

Maybe I will ask the question in a different way. 

There is a lot of interest in using 18650's, and of course, (excellent) guidance like this post on how to get bare cells, and posts on the risk aspects of improper handling and charging. (explosions)

So, for people like me that are interested in "using them safely", but not really able to "do this on our own", I have a few questions. 

1) Where can you buy a simple, standard, 2x18650 cells long - in series "battery pack" with the proper safety electronics for charge / discharge built in ? 

2) Is this a standard of any kind, or are all 18650 packs custom for OEM battery pack use ?

3) Where would a person buy a quality / not break the bank external charger for such a battery pack ?

Thanks for the assitance.


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## Doug S (Apr 7, 2004)

[ QUOTE ]
*HarryN said:*
Maybe I will ask the question in a different way. 

There is a lot of interest in using 18650's, and of course, (excellent) guidance like this post on how to get bare cells, and posts on the risk aspects of improper handling and charging. (explosions)

So, for people like me that are interested in "using them safely", but not really able to "do this on our own", I have a few questions. 

1) Where can you buy a simple, standard, 2x18650 cells long - in series "battery pack" with the proper safety electronics for charge / discharge built in ? 

2) Is this a standard of any kind, or are all 18650 packs custom for OEM battery pack use ?

3) Where would a person buy a quality / not break the bank external charger for such a battery pack ?

Thanks for the assitance. 

[/ QUOTE ]
Harry has some good questions. I have some less good answers. 

#1. I personally haven't seen this pack configuration but that doesn't mean it doesn't exist. I vaguely remember someone posting a link for a Li-ion flashlight that seemed to have a long [cells end to end] pack of some sort.

#2. Mostly custom. Some individual manufacturers have their own standard pack configurations [mostly targeted at the laptop market] but I don't know of standard packs used by multiple manufacturers. 

#3. If you know the nature of the pack internal protection circuitry, you could readily adapt a Li-ion charger intended for a different pack using a similar scheme. For example where the internal pack circuitry incorporates the charging termination function, the external charger typically is a current limited supply with an output in the range of 5V/cell. Chargers of this type can typically be found on Ebay for $1 plus $6-$7 S&H.

Let me add my own question to Harry's list. 
Does anyone know of a commercial charger that is specifically targeted at bare Li-ion cells. If so, does it claim [or does it's schematic show] independent protection against adverse outcome if the primary charging control circuitry fails in some manner? For a commercial product, it is not adequate IMHO to simply design a circuit that provides appropriate voltage and current limiting for charging bare cells without providing at least one additional independent layer of protection against failure of the primary charging control circuit.


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## Zorzi (Oct 13, 2015)

[ QUOTE ]<br />

#1. I personally haven't seen this pack configuration but that doesn't mean it doesn't exist. I vaguely remember someone posting a link for a Li-ion flashlight that seemed to have a long [cells end to end] pack of some sort.<br />

<br />

Not sure if this is what you saw, but the Nitecore MH2A comes with a long Nitecore Li-Ion pack with two 14400 cells that look in series, but that are actually connected in parallel, as the pack voltage is 3.7V. There is built-in charging circuitry in the flashlight. 

HTH, 

Zorzi


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## TinderBox (UK) (Oct 13, 2015)

On Post 1, I put the battery in a vice (do not short out the battery), With an metal rod ( I used an long screwdriver) running along the seam on one side of the battery and then just tighten the video a bit, then then put the rod on the other side on the battery losing the other seam and tighten the vice again.

John.


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