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proper balanced charging

  • NightRider Friday, October 10, 2014 2:50 PM Reply
    As reported by others, these batteries are made up of two series-connected lithium cells, so for proper charging the cells should be balance-charged, but these batteries have only two contacts so this is not possible.
    Reportedly, charging is done at 8.4V (2x4.2V) assuming that the cells are hopefully closely matched and thus reach the fully charged/discharged state concurrently. This is of course more critical during charging, because if the cells get badly unbalanced (something that can slowly happen over the lifespan of the battery) then the weaker cell will get overcharged and constitute a fire hazard.
    Thus, while charging, the weaker cell would reach the 4.2V "full" status earlier than the other stronger cell (which would have a lower voltage since it's actually charging properly and it's voltage is slowly rising as it should) and then continue rising to dangerous levels. As an example, let's assume the stronger cell has reached 3.6V, then the weaker cell would have 8.4-3.6=4.8V across it's terminals which is way too high!
    Of course a protection circuit should be installed to protect against such a scenario (hopefully even the cheap Lithium 9V bats have it) as well as also protecting against over-discharge, but I wonder - are there any 9V lithium bats with balance terminals that can help control the imbalance problem?
    I often install two rechargeable Lithium cells inside 9V operated equipment as a much longer-running solution (since I can use more powerful cells than available in 6F22 format bats) and balance charge them, but most of the time there isn't enough space inside the device for such a solution hence I'm searching for 9V lithiums with balance terminals.
    Can anyone contribute info on this issue?
    Cheers.
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    post edited by NightRider on 10/10/2014 at 2:56 PM
  • Xumixu Monday, October 5, 2015 4:51 AM Reply
    I wouldn't be bothered by "fire hazard", since batteries are quite resilient to overcharge (look on youtube), the capacity would be screwed thought. The real fire problem is if they get punctured.

    If you are still scared, try getting LIFeO4 "9V" batteries, they are way safer than LiPos.

    If you insist on balanced charging, you'd have to disassemble the battery, put a third lead, repackage the battery and charge them with a Smart Charger.

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