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Questions about Battery Memory

  1. Jan 6, 2010 #1
    Questions about Battery "Memory"

    I've heard that rechargeable NiCad batteries can be damaged so that they experience a large drop in voltage (and thus appear to be dead) before they are completely dead by being discharged to a point (like halfway) and then being recharged. Then I've heard that NiMH batteries do not suffer from this, then that they actually do, then that the whole thing is a myth... :devil: what do you guys think about this battery "memory" effect?
     
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  3. Jan 6, 2010 #2

    mgb_phys

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    Re: Questions about Battery "Memory"

    The strict "memory effect" is a myth, it effected certain early Ni-Cad batteries in very unusual circumstances.
    But there are many ways you can damage NiCad and NiMh batteries by improper charging, reducing their capacity.

    Simple intro here - http://www.greenbatteries.com/nibafa.html
    And an excellent and very complete guide - http://www.batteryuniversity.com/
     
  4. Jan 6, 2010 #3
    Re: Questions about Battery "Memory"

    Thanks for the info!

    After reading over the first FAQ, I seem to come to the conclusion that NiCd batteries are a bit more "vulnerable" than NiMh batteries when it comes to charging and discharging. Do you think that NiMh batteries are more "tolerant" in any way?

    Also, do you know if it is damaging to either battery type to partially charge it then discharge it fully?
     
  5. Jan 6, 2010 #4

    mgb_phys

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    Re: Questions about Battery "Memory"

    NiMh are a bit more robust.
    Partially discharing and recharging both types can (temporarily) reduce their capacity, but this can be restored by fully discharging and recharging.
    But you can permanently damage them by overcharging.
     
  6. Jan 6, 2010 #5
    Re: Questions about Battery "Memory"

    Ah I see, that's what I was hoping for.
     
  7. Jan 6, 2010 #6
    Re: Questions about Battery "Memory"

    A thought; I understand that, for example, a 1000mAh battery must be charged with 100mA for 10 hours to be fully charged. So, would charging it with 100mA for 5 hours give it a 500mAh current?
     
  8. Jan 6, 2010 #7

    mgb_phys

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    Re: Questions about Battery "Memory"

    Roughly yes.
    The charging curve isn't quite linear (depends on how full the battery is) and you can't push it too far - you can't charge it in 1min with 60Amps for instance!

    ps. you can't say a 500mAh 'current', mAh is an amount of energy so you shoudl say a 500mAh 'charge'
     
  9. Jan 6, 2010 #8
    Re: Questions about Battery "Memory"

    Ah. Roughly how non-linear is it?

    Got it.
     
  10. Jan 6, 2010 #9
    Re: Questions about Battery "Memory"

    It is by no means a "myth" with respect to NiCads. As a heavy NiCad user in the 80s, we had to factor it's effects on a continuing basis.

     
  11. Jan 7, 2010 #10
    Re: Questions about Battery "Memory"

    Ah. I did read, however, that it was something that occurred when a NiCad was charged and discharged to at a quite precise point many times (such as in satellites), and unlikely to occur in consumer electronics.
     
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