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Thread: Battery Marriage

  1. #1
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    Battery Marriage



    So I've been doing some research in to pairing/marrying batteries and thought I would pass on what I've gathered and for input from others to fill in the blanks.

    So basically we pair our batteries up due to with each charge you lose a small amount of energy, why we replace our batteries at one point. If one battery is older than another it means the other battery has to pick up the slack and work harder.

    This is especially important in a series mod, this is because the first battery in the series will take the grunt of the force so you want to alternate your batteries positions. If an old and a new battery are used together, itís possible for the old one to be discharged below the normal 3.2v causing damage to the battery and maybe your device.

    As with a parallel mod, using an old battery with a new battery will mean due to that small loss of energy over time one, your new battery will be taking in extra workload and taking in higher amps possibly.

    Battery safety to me is really important as I regularly like to build below .1 ohm and at this point in time some of the biggest negativity surrounding vaping is exploding batteries in the media. This is just what I have found, if anyone has any more information or if I've made a mistake, let me know

  2. #2
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    Completely agree, it's quite difficult to cause thermal runaway (boom) without a dead short but venting is more likely from over stressing a battery, ventings abit less violent but still not fun having 150c+ gas spraying everywhere but sure beats 900c+ fire balls and shrapnel from thermal runaway.

    Good idea to check battery voltages when taking them off the charger to make sure they are fairly even, 0.05v difference is okay but anymore then that just keep an eye on them to make sure they don't drift any further.


    Sent from my MotoG3 using Tapatalk

  3. #3
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    I actually started a thread about this a while back, and let it die because I found that so long as you are able to pay some attention to what's going back into the cells once they're discharged and try and keep 'like' cells together, that's enough.

    These 18650 cells are surprisingly consistent, so getting a matched pair shouldn't be difficult so long as you start out with a handful of them, mark them and rotate them with each other for a few cycles in the bit of kit they'll be used in to see how they work with each other, and pick the two that like each other best based on how much juice you're putting back into them once they're used as a pair.

    Very unscientific, but it seems to be perfectly adequate for these cells. I've got one reasonably matched pair of VTC5, my 2 x VTC5a talk to each other well and the other two VTC5 are in single cell devices only, as are the 5a now.

    I don't need anything more than what a single cell can deliver. About the only thing I'd suggest is that if you use cells in series without monitoring or regulation then you do need to pay special attention to what's going on with those cells each and every time. And if a monitoring and regulated mod uses series batteries without monitoring each cell individually, find one that does and save any worries.

    As far as safety really goes, so long as the cells you use are capable of delivering sufficient current then they should be fine. You can push the envelope if you wish to, but it's a case of "if you need to ask, you probably shouldn't be doing it". Goes for a lot of things in life, many aren't smart enough to work it out.

    Oh, the whole 'new battery picks up the slack' thing might not be quite true. It might be, but always used to be the strong cell(s) would be limited by the weaker cell, and the weaker cell being pushing to it's limit constantly would fail much faster than it normally would. In Nicad and NiMH packs, that would often result in a cell that ended up being reverse charged by the rest of the pack and killed off. In these lithium cells, it may result in full (0v) discharge which makes the cell just as dead. I see no reason why the situation would change with a change in battery chemistry, but it could. I don't know for sure.

    Stu.

  4. #4
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    Quote Originally Posted by Schtoo View Post
    Oh, the whole 'new battery picks up the slack' thing might not be quite true. It might be, but always used to be the strong cell(s) would be limited by the weaker cell, and the weaker cell being pushing to it's limit constantly would fail much faster than it normally would. In Nicad and NiMH packs, that would often result in a cell that ended up being reverse charged by the rest of the pack and killed off. In these lithium cells, it may result in full (0v) discharge which makes the cell just as dead. I see no reason why the situation would change with a change in battery chemistry, but it could. I don't know for sure.
    My understanding is that a cell that has collapsed can indeed be put into a reverse polarity/charge condition. Modern regulated mods should never let this happen, but there have been a few bad ones (looking at you, dot.mod).

    Such a cell, since it holds no charge (energy) I suspect is in no danger of catching fire, however reverse polarity will damage the plates, so it should never, ever, be charged again if that is the case.

    I agree, careful monitoring of the cells is all that is required. They should be roughly the same voltage at all times. If they keep getting out of step it indicates that one cell is weaker than the other. It's still safe, as long as you don't discharge either/any cell below 3.2V (I always recommend 3.4V). Individual cell monitoring and cut off in the mod is ideal.
    Last edited by fabricator4; 06-11-17 at 06:48 PM.
    Wombats1 likes this.
    Chris: Tobacco free since 17:00 15th March 2013.


  5. #5
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    ChasK likes this.
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