Charging a Car Battery
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  1. #1
    Senior Member cptrout's Avatar
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    A couple days ago my truck would not turn over so I called AAA and they came out and gave me jump. The guy told me my battery did not have a full charge. I drove home, 15 minutes, turned off engine and then restarted it and it fired right up. Later the nite it would not turn over again.

    I have a 12v battery charger that I’ve had for years and have never used so I thought I put it to use.

    The charger has a 2 amp and 10 amp selector switch and I set it to 2 amp. I connected the connectors and plugged in the charger. There is an analog gauge on the charger labeled DC Amperes that goes from 0 to 15. When I select 2 amp the gauge reads 4 and when I select 10 amp the gauge reads 12.5.

    Can someone please explain this. I really don’t want to blow anything up or damage my battery

  2. #2
    Senior Member jbfla's Avatar
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    Hi cp,



    You didn't say how old the battery is, but if it will accept that much amperage



    it's most likely completely dead or has a shorted out cell.



    Use a voltmeter, if you have one, to check the voltage. 11 volts or less, the



    battery is dead.



    Check the water level and fill if necessary, then put your charger on the battery.



    The amp meter on the charger should gradually decrease as the battery accepts



    the charge. If it doesn't decrease, it's time to buy a new battery.



    If you can jump you battery again and get the truck started, put the voltmeter on



    the battery. It should read about 14+ volts. That will tell you if your



    alternator is working.



    jb
    2018 Triumph Street Twin..............2016 CB500F
    2014 XT250 ..................................2008 H-D Softail Deluxe
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  3. #3
    Banned qwerty's Avatar
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    Advance Auto Parts does a simple electrical system test for free.




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  5. #4
    Senior Member mrlmd's Avatar
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    Leave the charger on for 8-10 hours or so, the voltage should slowly rise if the battery is being charged properly. It may rise to as much as 13-13.5+V at the peak if the charger is working. Measure the voltage at least a half hour after you finish charging it (to eliminate or let dissipate the "surface charge"). it should read 12.6 V. Measure it again the next day, it should hold it's charge. To see if the battery is any good, after it's fully charged, you can get it load tested for free at any garage or auto parts store or battery place. They'll do it for free because if it's bad they would like to sell you a new one.

    If your car was jump started, riding it for only 15 min. will not recharge it back to it's full capacity so that's why it was dead again the next day.

  6. #5
    Senior Member assquatch20's Avatar
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    Now that you know what to do, report back with your findings. A bad voltage regulator gave me an issue that seemed like the battery went belly up overnight.

  7. #6
    Senior Member cptrout's Avatar
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    Thanks for getting back to me guys with the help, I really appreciate it and sorry for the slow update/response.

    My question was more about my battery charger but I did end up pulling the battery and taking it to Orielly's to have it checked. The battery had a bad cell and I replaced it. $47, pro-rated for a new battery and everything is good now.



    As for the battery charger help of which jbfla did partially answer and I thank you but I still am interested to know why when I charged the battery on the 2 amps the gauge read 4 and when I selected 10 amp the gauge read 12.5?

    Was I getting this reading because the battery had a bad cell or does it sound like my charger is defective?

    My charger is a Schumacher that my grandfather gave me 10 years ago and I had NEVER used till this incident. Thanks again.

  8. #7
    Banned qwerty's Avatar
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    Consumer electronics are notoriously wide-ranging. It is not unusual for a specific component to have a 30% plus or minus range of tolerance. for instance, a resistor marked 1000 ohms may actually measure anywhere from 700 to 1300 ohms and still be considered in spec. Aero-space and mil-spec components can and do have much closer tolerances, but you pay heavily for those capabilities. Therefore, either your particular charger is made from parts that allow a 25% or more deviance from rated output, which is actually rather common, the meter on your charger is inaccurate, which is rather common, or some combination of the two, which is also rather common. Don't worry, be happy. All is screwed up with the world. Perfectly normal.




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