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  1. #1
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    Need a quick tutorial on replacing a bad cell.

    Hey everyone, new to the DIY forum (not MTBR) so feel free to point me to any posts/threads I didn't find in my search.

    I've got a the generic Chinese light with the Cree XML. Light head just stopped working with my battery pack (works with another one I borrowed) Charger flashes red when the pack is plugged in. I'm going to double check that its not the charger, but I'm almost certain its the battery.

    I'd like to open up the battery pack and replace the bad cell(s). I'm reasonably savvy with electronics (mostly audio/video and automotive/home). I have a volt meter and soldering iron.

    Firstly, what and I going to see when I open it up? Are the cells typically connected via solder? Circuit board? Leads? etc...
    Secondly, what will be the best test for checking my cells? Voltage? Current? etc..

    If someone could quickly just tell me the process for checking the cells that would be great!

    thanks!

  2. #2
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    Batteries are usually connected with tabs/strips that are welded to the cells when built in bulk:

    Here's a couple of pics of various vintages of Magischine batteries dissected:

    GeoManGear Rocks

    and here:

    From this thread: MagicShine battery dissection / testing

  3. #3
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    As far as testing cells individually, just use your voltmeter on each battery individually. Hopefully you'll find one that is waaay below the others. that's probably the bad one.

    You could, however have a cell that shows voltage, but just doesn't have any capacity - you'd need to figure out a way to put a load on each cell while monitoring voltage to see if any drop out quickly.

    As you see, there is also a potential issue with the protection circuitry in the battery itself. if you can test the cells and they pass, then replace the protection board with another and you might be good to go.

  4. #4
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    thanks for all the help guys.
    Should I be able to test my connection from the battery pack with a volt meter?

  5. #5
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    Yes, unless the PCB is the issue and it isn't passing voltage.

  6. #6
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    Also - if you have a Batteries Plus store near you, they usually can rebuild/replace a cell in a pack with the proper spot welds and such.

  7. #7
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    Plan B. Split my 4 cell pack into two 2-cell packs???

    on to plan B.
    My buddy just went to all-in-one lights and gave me 2 Geoman Magicshine batteries (the new replacement ones) as well as a light head (the one with a large center light and two smaller ones)
    I can now use those batteries with my existing light head.
    I'd like to get a light head for the helmet and just had the idea to take my old battery pack and turn it into two smaller packs.
    So here's where I need help:
    Which circuit board would I likely need to use these two cells with something Magicshine-ish on the helmet?
    Best spot to purchase the circuit board and wiring connector?
    Any ideas for scavenging the 3 led Magicshine I have to make it into a small headlamp/helmet light?

    attached are a pic of my 1st battery pack and the lighthead.
    Attached Thumbnails Attached Thumbnails Need a quick tutorial on replacing a bad cell.-photo.jpg  

    Need a quick tutorial on replacing a bad cell.-photo2.jpg  


  8. #8
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    Quote Originally Posted by gcavy1 View Post
    Which circuit board would I likely need to use these two cells with something Magicshine-ish on the helmet?
    You use the same board for the 2-battery pack and the 4-battery pack, since they are both 7.4V. Dealextreme have the boards.

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