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Thread: Unwrapping 2x18650 batteries connected in series

  1. #1

    Default Unwrapping 2x18650 batteries connected in series

    Before I started getting serious about flashlights, I bought two cheaper ones which both lasted about two months before the switch of each one broke. This is the second light that I got:




    It seems that two 18650s are wrapped together, with an exaggerated capacity (4400mAh) that isn't possible in a serial configuration.

    Here's a close up of the other side:



    I'd be interested in removing the wrapper, to see what is underneath. Is it safe to do so? Is there anything I need to be careful about?

    (That's probably a 'silly' question, but I'd rather be safe than sorry!)

  2. #2
    HKJ's Avatar
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    Default Re: Unwrapping 2x18650 batteries connected in series

    I would expect the batteries are connected in parallel with some metal strips.
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  3. #3
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    Default Re: Unwrapping 2x18650 batteries connected in series

    Hello Bright Bird,

    You need to measure the voltage. As Henrik indicated if the voltage is around 4 volts, the cells are connected in parallel. That means it is like having a single high capacity cell. If the voltage is around 8 volts then the cells are in series.

    In this case, looks may be deceiving.

    Tom
    Behind every Great man there's always a woman rolling her eyes...

    Most batteries don't die - they are tortured to near death, then murdered...

  4. #4

    Default Re: Unwrapping 2x18650 batteries connected in series

    Quote Originally Posted by HKJ View Post
    I would expect the batteries are connected in parallel with some metal strips.
    I was thinking along those lines, but then thought that there is probably not enough space for metal strips with a low enough resistance. But with you being the battery expert on here, I trust that you are right! Guess I'll be finding out shortly.

    Quote Originally Posted by SilverFox View Post
    Hello Bright Bird,

    You need to measure the voltage. As Henrik indicated if the voltage is around 4 volts, the cells are connected in parallel. That means it is like having a single high capacity cell. If the voltage is around 8 volts then the cells are in series.

    In this case, looks may be deceiving.

    Tom
    I'm not actually sure whether I want to recharge it as it is (which would only be possible inside the flashlight). At the time I thought that rechargeable flashlights sounded like a cool idea, but meanwhile I am glad that I've got my chargers! Of course, I'll pump some juice into them after I've separated both batteries from each other to test their voltage and capacity.

    Yes, my Olight SR52 uses three 18650s in a parallel configuration, so it runs on a voltage of (initially) 4.2V, and with a capacity of 10.2Ah, whereas the Thrunite TN4A that I recently bought combines the voltage of the 4 AA cells in a serial configuration, while maintaining the capacity of each individual battery (1900mAh).

  5. #5

    Default Re: Unwrapping 2x18650 batteries connected in series

    Here we go ... the results of my experiment.

    Not much to see on the individual wrappers except for a barcode and +/- markings, and there is indeed a metal strip connecting the anodes with each other.



    And a connection between the cathodes as well.



    There was also a metal strip on the other side of the battery, as part of the parallel configuration.

    A button top with spacer disc:



    And finally the PCB (on the positive end of the second battery):



    When I separated the batteries, the metal strip of one battery must have short-circuited it, as something suddenly got very hot so that I had to drop it. The battery itself also felt a bit warm afterwards. Is that battery still safe to recharge? Or should I abandon my experiment at this point? They both show 4.05V on my MM (although I'd need to find the instructions to figure out how to check their capacity). Before popping them into a charger, I'd also have to find a way to get rid of whatever is stuck on the electrodes.

  6. #6
    Silver Moderator
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    Default Re: Unwrapping 2x18650 batteries connected in series

    Hello Bright Bird,

    Interesting configuring...

    It sounds like you had a momentary short that caused a high current flow. This should not be a problem but keep an eye on the cells the first time you charge them.

    Tom
    Behind every Great man there's always a woman rolling her eyes...

    Most batteries don't die - they are tortured to near death, then murdered...

  7. #7

    Default Re: Unwrapping 2x18650 batteries connected in series

    OK, will do.

    There's a bit of the metal strip that's still stuck pretty stubbornly to the negative ends, but I'll try to find a craft knife tomorrow, and some solvent. Not sure about what looks like insulation material around the outside of the + poles, but I guess it won't do any harm to leave that, as the charger just needs to be in contact with the middle.

  8. #8

    Default Re: Unwrapping 2x18650 batteries connected in series

    I've had to abandon my experiment. There are still remnants of the metal strip that was glued (or spot-welded? Not sure how to tell) on both cathodes and I don't think that I'll be able to get the surface smooth enough for a good contact with the poles of the charger. And it seems that I've managed to get a few dents in the surface, as well, which doesn't make it very encouraging to continue.

    As curious as I am, I don't want to be the cat that gets killed by it! 🙀

  9. #9

    Default Re: Unwrapping 2x18650 batteries connected in series

    It is GREEN but it looks blue to me.

    Mike

  10. #10
    Unenlightened
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    Default Re: Unwrapping 2x18650 batteries connected in series

    interesting configuration. i guess the "3.7V" gives it away as being in parallel.
    wonder how common this is... anybody with a decent charger would probably see this as an inconvenience (as much as they're more likely to use the charger than charge this in the flashlight


    lol @ mike

  11. #11

    Default Re: Unwrapping 2x18650 batteries connected in series

    Quote Originally Posted by LloydV View Post
    interesting configuration. i guess the "3.7V" gives it away as being in parallel.
    wonder how common this is... anybody with a decent charger would probably see this as an inconvenience (as much as they're more likely to use the charger than charge this in the flashlight


    lol @ mike

    ... and just think of the lack of available spare batteries - anyone with the skills to duplicate that configuration is probably unlikely to buy a cheap T6 flashlight. On the other hand, considering that it only lasted me a couple of months before the switch broke, for most people the batteries will probably last longer than the light itself!

    P.S I'm afraid your humour is lost on me, Mike - I'm not very good with cultural references (if that's what it is)...
    Last edited by Bright Bird; 07-19-2017 at 07:50 PM.

  12. #12

    Default Re: Unwrapping 2x18650 batteries connected in series

    He was lol-ing me

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