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Can a battery that is completely shot still have a full voltage?

  1. Jul 22, 2013 #1
    This is sort of an engineering question and sort of not but it involves me possible replacing the lithium-ion battery in my iPod Touch. My iPod will not turn on no matter what I do. My iPod says that there is no battery life left in the battery, yet when I took it apart and removed the battery, my volt-meter shows that the battery has a voltage of exactly 3.7 volts which is the battery's factory voltage. To me it seems that it could be a shot battery but the fact that the battery has 3.7 volts says otherwise. I want to know if it is my battery that is the problem before I pay to order a replacement.
     
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  3. Jul 22, 2013 #2

    phinds

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    A battery with zero load (and a multi-meter is very close to zero load) can show full charge but as soon as you add a load, the voltage can drop precipitously if the battery is basically depleted.

    You need to get a resistor that simulates roughly the load of the ipod and put it across the batter and THEN see what the voltage reading is.
     
  4. Jul 22, 2013 #3

    Integral

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    I will quibble with the use of charge here. A voltmeter can never tell you about the charge, it only shows potential. So a dead battery when using a "good" voltmeter will show full potential. As soon as you attempt to draw current (charge) from the battery the terminal voltage will drop.

    A "good" voltmeter, that is one with a very high input impedance is NOT a "good" meter to check batteries with. Better off with a old analog meter that draws a measurable current for checking batteries.
     
  5. Jul 22, 2013 #4
    Thanks for the responses, that makes sense how the volt-meter won't really show whether or not it is a good battery. How about I try removing the battery again and try using to power a simple LED driver? Would seeing if the LED lights up significantly be a fairly good determination of whether or on the battery is completely shot?
     
  6. Jul 22, 2013 #5

    phinds

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    I absolutely agree. I mis-spoke. Meant to say voltage, not charge. My dyslexia kicking in once again.
     
  7. Jul 22, 2013 #6

    phinds

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    Yeah, sounds good to me.
     
  8. Jul 22, 2013 #7

    Integral

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    Check terminal voltage while it is drawing current.

    The best route is just to replace the battery, rather then spending a lot of time on something that is obviously bad.
     
  9. Jul 22, 2013 #8

    dlgoff

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  10. Jul 22, 2013 #9
    It is just that I want to make absolutely sure that the battery is the problem before ordering one. I know that they aren't too expensive, I just don't have a large budget. I will test the battery as you have suggested tomorrow.
     
  11. Jul 22, 2013 #10
    Thanks for that post. That looks like a site that will be a good reference for me.
     
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