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  1. #1
    sandermarijn's Avatar
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    Is a battery's initial voltage a good measure of life expectancy?

    I have some 2CR5 batteries dated 2008, as well as some newer ones (2020). All are unused. The older batteries have an open-circuit voltage of 7.06 V, the 2020 batteries are 7.08 V.

    Is the measured voltage a reliable measure of life span? IOW, can I rely on these older batteries?

    In a related question: how accurate are the expiry dates of lithium batteries? Like with a pack of salt or more like with milk?

    Thanks guys (and the occasional girl),
    Sander

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    No, it's not.

    What is called an "Open Voltage" - a measure of voltage when there is no load attached to it, is usually right at the specification. By the time that drops lower, it's seriously degraded.

    What's important is the voltage under load. Many battery checker uses small register as a simulated load, then measure the voltage.

    I'm guessing you used digital multi-meter. If that's the case, unless it has a special battery check mode, you are measuring an open voltage. Plus, the accuracy of many meters like that are so that .02 volt difference is within the margin of error.
    Develop, stop, fix.... wait.... where's my film?

  3. #3
    Steve Smith's Avatar
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    Quote Originally Posted by sandermarijn View Post
    In a related question: how accurate are the expiry dates of lithium batteries?
    The voltage isn't suddenly going to drop to zero at one minute past midnight on the expiry date.

    If they measure close to seven volts open circuit, I would consider them as good as new and use them without worrying about them.


    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  4. #4
    sandermarijn's Avatar
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    Quote Originally Posted by tkamiya View Post
    What is called an "Open Voltage" - a measure of voltage when there is no load attached to it, is usually right at the specification. By the time that drops lower, it's seriously degraded.
    Sounds good .

    Quote Originally Posted by tkamiya View Post
    I'm guessing you used digital multi-meter. If that's the case, unless it has a special battery check mode, you are measuring an open voltage. Plus, the accuracy of many meters like that are so that .02 volt difference is within the margin of error.
    Yes, cheapy digital multimeter. No battery check mode on those, maybe I should get a real one. Of course my EOS does have a built-in battery meter, but that one isn't very accurate I suppose ("OK, almost dead, dead").

    I wonder, does the open-circuit voltage ever drop, also long after the expiry date has passed? IOW, is there a situation thinkable wherein the open voltage does represent a faithful indication of life left? How long past expiry will it typically take a lithium battery to show such significant open voltage degrading?

  5. #5
    sandermarijn's Avatar
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    Quote Originally Posted by Steve Smith View Post
    The voltage isn't suddenly going to drop to zero at one minute past midnight on the expiry date.
    Happened to me with a pack of salt the other day .

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    dupe

    How the heck do you delete a post???
    “Wise men talk because they have something to say; fools, because they have to say something.” - Plato

  7. #7
    Leigh B's Avatar
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    Most modern battery technologies hold nominal voltage pretty closely until end-of-life. That's true both under load and open-circuit.

    Common zinc-carbon batteries like D-cells in flashlights, are an exception. The voltage drops uniformly during use, and end-of-life is application-dependent.

    Your 2008 batteries are probably still usable, but don't put them in a pacemaker.

    - Leigh
    “Wise men talk because they have something to say; fools, because they have to say something.” - Plato

  8. #8
    sandermarijn's Avatar
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    Quote Originally Posted by Leigh B View Post
    Your 2008 batteries are probably still usable, but don't put them in a pacemaker.
    Or in a space shuttle.

  9. #9
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    just hock it up to some load(optimally similar to one they will be used with) and monitor voltage for 10 min or so if it is not good you will see right away.
    Multum egerunt, qui ante nos fuerunt, sed non peregedunt.

  10. #10
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    The other thing is that since it's a lithium, the discharge curve is pretty flat, i.e. the voltage doesn't vary much during the normal life of the battery. Once it's exhausted, the voltage drops off quite precipitously.

    Another vote for "probably fine just don't trust them much".

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