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Need help diy a power bank

Discussion in 'Power Electronics' started by mikey5791, Feb 7, 2021.

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  1. mikey5791


    Jun 7, 2013
    Hi friends,
    Got this simple power bank of 8800mAh capacity but the inside battery seems to be failing. It is not taking any more useful charge. The dmm measured the battery reading about 0.17vdc. The input is rated at 5v 2.0A. I was thinking about replacing the failed battery with some extra batteries from my used laptop battery pack.
    The laptop battery pack is AL15A32( rating 14.8v 2350mAh) consisted of 4 series joined 18650 type li ion battery. However, one of the battery showed only 0.15vdc but the remaining 3 are still within 3.77v to 4.21vdc. Is it possible and safe to cut off the 3 li ion battery and solder to the power bank connector and try charging with an off the shelf 5v 1.5A phone charger? I wish to rebuild this set of battery pack as a power bank and hope for any advice if this can be done.

    Attached Files:

  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    The battery in the power bank seems to be of the flat pouch type. That one would be a Li-Ion cell with a nominal voltage of ~3.7 V (label is possibly on the reverse side of the battery.
    This pouch should be replaceable by another Li-Ion cell that fits the case.

    1. If you do so, you'll have to connect the remaining 3 batteries in parallel to achieve the 3.7 V (approx.). In a series connection the battery voltage is way too high.
    2. Cutting the battery stack may be straightforward. Soldering Lithium batteries is not recommended. They easily overheat and can catch fire. Although you'll be able to find "instructions" on how to solder these batteries, it really is not recommended. The correct way is by spot welding which requires a special spot welder. If you are lucky there will be short strips of nickel tabs left over from the original weld after cutting the stack. In that case you can solder to these tabs. Works fast to prevent the heat of the soldering to enter the batteries.
    3. Last not least you'll have to fit the new battery mechanically into the case of the power bank - or find a new, bigger case.
    Martaine2005 likes this.
  3. mikey5791


    Jun 7, 2013
    Hi Harald,
    Thanks for reply.
    I will look for a bigger case to fit in the battery pack before i attempt this project.
    Thanks for the advice.
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