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Thread: Battery Tester

  1. #1
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    Battery Tester

    I have a battery tester with the following instructions:

    " The level of charge in a battery is measured by checking the exact voltage given out by the
    battery. If the battery had just been charged, or used in the vehicle recently then the following course should be followed:

    *Switch on headlight for a short period (approx. 1-2 minutes).
    *Switch off headlight and disconnect battery from the vehicle.
    *Wait 10 minutes.
    *Connect the Battery Tester to the battery. The LED's will indicate the level of charge in the battery.

    If the battery is not fitted in a vehicle, and has not been used for several hours, you can just connect the battery
    tester and check the reading".

    ************************************************** ***************************************
    As you can see, it instructs you to "Disconnect battery from the vehicle"

    What is the main reason for disconnecting the battery before testing it? What harm can result from merely connecting the clips of the tester to the CONNECTED battery?????????
    Does anyone own a battery tester?





  2. #2
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    Re: Battery Tester

    There is usually a small drain on the battery just by being connected. Stuff like the radio station presets and keyless entry. On the high-end luxury cars, this is even greater because of features like keyless go, where it looks for a transponder to unlock & start the car for you.

    Chip H.

    Former owner: 2012 Honda Civic LX, 2006 Honda Ridgeline RTL, 2000 Honda CR-V EX, 2003 MINI Cooper S, 1992 Honda Accord LX, 1999 Mercedes ML-320, 1995 VW Jetta GLX, 1991 Mercury Capri XR2, 1981 Mercury Zephyr, 1975 Chevrolet Impala

  3. #3
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    Re: Battery Tester

    Quote Originally Posted by chiph
    There is usually a small drain on the battery just by being connected. Stuff like the radio station presets and keyless entry. On the high-end luxury cars, this is even greater because of features like keyless go, where it looks for a transponder to unlock & start the car for you.

    Chip H.
    I see, but my car is one of the older ones and has none of those features you find in modern cars like keyless entry
    etc. Anyhow, I now understand the reason for unhooking the battery before testing it.

  4. #4
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    Re: Battery Tester

    >>I see, but my car is one of the older ones and has none of those features you find in modern cars like keyless entry
    etc. Anyhow, I now understand the reason for unhooking the battery before testing it. <<

    And after using this tester, you only know the level of charge which tells you very little about the capacity of the battery. Battery capacity is the improtant test and will let you know how close to the end of the battery's useful life you are.
    That test is done with a small computerized unit and will give you a CCA (cold cranking amp) reading that you can compare against the original CCA of the battery. This test can be done even on a completely discgarged battery. Most Ford, Honda, and Toyota dealers have the unit. It also is used at Sears and Sam's Club and probably a bunch of other places.


  5. #5
    DonTom
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    Re: Battery Tester

    That's not the reason. The few mills draw from a battery will have no effect on the battery tester. Most likely, the battery tester draws a lot of current and they think in some rare cases, the surge of connecting and disconnecting the tester could be harmful to some of the electronics in the vehicle. The safest way is to disconnect the battery.

    -Don-



    Quote Originally Posted by chiph
    There is usually a small drain on the battery just by being connected. Stuff like the radio station presets and keyless entry. On the high-end luxury cars, this is even greater because of features like keyless go, where it looks for a transponder to unlock & start the car for you.

    Chip H.

  6. #6
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    Re: Battery Tester

    >>That's not the reason. The few mills draw from a battery will have no effect on the battery tester. Most likely, the battery tester draws a lot of current and they think in some rare cases, the surge of connecting and disconnecting the tester could be harmful to some of the electronics in the vehicle. The safest way is to disconnect the battery.<<

    With the type of tester he's using, following the instructions is necessary. The problem is accuracy and that type of tester is only about 80% accurate. The computerized ones that will test the batteyr regardless of state of charge are 99% ACCURATE and will tell you if a replacement is necessary in about 30 seconds.They measure CCA and compare the readings to the size of the original when new.


  7. #7
    DonTom
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    Re: Battery Tester

    With that tester, how long does it take to test the battery? Long enough that a few mills will make a difference?
    IAC, we all agree to disconnect the battery. Perhaps for more than one reason.

    -Don-


    Quote Originally Posted by Jim Rose
    >>That's not the reason. The few mills draw from a battery will have no effect on the battery tester. Most likely, the battery tester draws a lot of current and they think in some rare cases, the surge of connecting and disconnecting the tester could be harmful to some of the electronics in the vehicle. The safest way is to disconnect the battery.<<

    With the type of tester he's using, following the instructions is necessary. The problem is accuracy and that type of tester is only about 80% accurate. The computerized ones that will test the batteyr regardless of state of charge are 99% ACCURATE and will tell you if a replacement is necessary in about 30 seconds.They measure CCA and compare the readings to the size of the original when new.


  8. #8
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    Re: Battery Tester

    >>With that tester, how long does it take to test the battery? Long enough that a few mills will make a difference?
    IAC, we all agree to disconnect the battery. Perhaps for more than one reason. <<

    The computerized tester only requires that you be able to open the hood and have everything turned off. The few mills used by the electronics on the vehicle makes no difference.
    I spent 28 years with the company that designed and built the original computerized battery tester. It was originally built into a large diagnostic computer and incorporated in the complete test proceedure for the engine.
    Sears asked us to build it as a stand alone unit-- we did and they equipped each automotive center with at least one unit. It cut their warranty rate to less than 1%.Prior to this unit, a battery had to be fully charged to be properly tested. That took a lot of time and most customers wouldn't wait ---

  9. #9
    DonTom
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    Re: Battery Tester

    "The computerized tester"


    I was asking about the cheaper tester. How long does it take to test a battery?

    -Don-

  10. #10
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    Re: Battery Tester

    >>I was asking about the cheaper tester. How long does it take to test a battery?<<

    If the battery is fully charged, it should take about 15-30 seconds, depending upon the load it uses. The problem is, you still don't have a real capacity test and it's (when in the hands of an expert) only 80% accurate at best!


  11. #11
    DonTom
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    Re: Battery Tester

    How does a load of a few milliamperes have any effect on a 30 second battery test? I seem to be missing how this thing works.

    -Don-




    Quote Originally Posted by Jim Rose
    >>I was asking about the cheaper tester. How long does it take to test a battery?<<

    If the battery is fully charged, it should take about 15-30 seconds, depending upon the load it uses. The problem is, you still don't have a real capacity test and it's (when in the hands of an expert) only 80% accurate at best!


  12. #12
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    Re: Battery Tester

    >>How does a load of a few milliamperes have any effect on a 30 second battery test? I seem to be missing how this thing works.<<

    It shouldn't have any affect-- And to me neither will the test have any affect on my decision to replace the battery. That tester only measures state of charge. Not capacity, and capacity is the important factor in testing an automotive battery.
    A sulphated battery, after following their test proceedure will usually show as good!

  13. #13
    DonTom
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    Re: Battery Tester

    A sulphated battery, after following their test proceedure will usually show as good!

    IMO, the only real good test on a lead-acid battery is to not test it at all and replace it about every three and a half years. -Don-


  14. #14
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    Re: Battery Tester

    >>IMO, the only real good test on a lead-acid battery is to not test it at all and replace it about every three and a half years<<

    That's an OK thought, but, if a decent battery test is available, why throw away a perfectly good battery? I said a "decent test", one that reads capacity---

  15. #15
    DonTom
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    Re: Battery Tester

    That's an OK thought, but, if a decent battery test is available, why throw away a perfectly good battery? I said a "decent test", one that reads capacity

    Because even if it passes the test, it's unlikely to have more than about two years left. My way, any battery problem ever is quite unlikely.
    -Don-


  16. #16
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    Re: Battery Tester

    >>Because even if it passes the test, it's unlikely to have more than about two years left. My way, any battery problem ever is quite unlikely<<

    As long as one is willing to pay the price--- To me, it's just wasted money to replace something that is OK and has 80% or more of it's original capacity!

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