How to discharge a battery?

Discussion in 'General Electronics Chat' started by UnnamedUser159, Jan 25, 2018.

  1. UnnamedUser159

    Thread Starter Member

    May 3, 2016
    426
    2
    hi.
    i own little IT service.
    i have not little mobile phone batteries.
    Want to discharge them first (maybe with Resistance ? ) and then put it on my universal mobile phone batteries charger to make them full.

    Is this with Resistance right and what to be the value and maximum heat over it in watts?
     
  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    7,513
    1,239
    Ideally you would be better using a Constant Current discharge, this will discharge it linearly until it is flat.

    With a resistor the current will decrease as it gets lower in voltage, and will take longer, if you want to use a resistor try a 16 ohms 5W.

    Discharge the cells at 10% of their capacity, so if the battery is 3600mA, use 330-360mA.
     
  3. crutschow

    Expert

    Mar 14, 2008
    19,748
    5,524
    Why do you think you need to discharge them first?
     
  4. MrSoftware

    Well-Known Member

    Oct 29, 2013
    1,051
    292
    And what chemestry are they (NiCd, Lipo, etc..)? Some chemistries should be occasionally discharged, most modern chemestries do not like being fully discharged.
     
    ericgibbs likes this.
  5. UnnamedUser159

    Thread Starter Member

    May 3, 2016
    426
    2
    the idea is selling maybe...this way they only collect dust

    want to discharge them like the battery is pluged in phone and on screen there was a message "low battery"

    then put it on the charger and see the battery is charging 2-3 hours for example so i am making the conclusion "the battery is relative good"
     
  6. MrSoftware

    Well-Known Member

    Oct 29, 2013
    1,051
    292
    Ahh a battery tester! That makes sense. Do you want to track how much energy comes out of the battery as it discharges?
     
  7. ian field

    AAC Fanatic!

    Oct 27, 2012
    6,205
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    That's what I was wondering - nickel chemistry likes the occasional complete discharge, but there's a risk that one cell gives up first and the others push reverse charge through it. that turns a weak cell into a shorted one. Particularly on cordless tools - they're not a good approximation to constant current charger. The lower terminal voltage causes an increase in charge current and more shorted cells - this usually kills the charger.

    Lithium has a minimum allowable terminal voltage. My e-cig gets over discharged occasionally - the consequences don't seem to be all that devastating.
     
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