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My 12v Battery test???

Discussion in 'Gen 2 Prius Technical Discussion' started by ski.dive, Jun 14, 2019.

  1. ski.dive

    ski.dive Active Member

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    Yellow Top Battery is approx. 5 years old.

    This morning, I tested my battery with engine off === It shows 11.5V

    I then tested my battery with the engine on === It shows 14.3V

    Are 11.5V first thing in the morning too low, is my 12V battery getting weak?
     
    #1 ski.dive, Jun 14, 2019
  2. jb in NE

    jb in NE Senior Member

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    11.5V shows that the battery is not fully charged. Either it is not being charged or is not holding a charge. With 14.3 V available with the engine ON, this should be sufficient to charge the battery given enough time. The manufacturer's website has some good information to review. A load test would be your next best step, but with a 5 year old battery it is may be that the battery is at the end of its useful life.

    Recommended Battery Voltage- YELLOWTOP®, REDTOP®, BLUETOP® | Support | OPTIMA® Batteries

    "Fully charged, engine not running, starting batteries (all REDTOP® or BLUETOP® 34M) should measure about 12.6 volts to 12.8 volts. Deep-cycle batteries, including all YELLOWTOP® and dual-purpose BLUETOP batteries, should measure approximately 13.0 to13.2 volts."

    http://d26maze4pb6to3.cloudfront.net/optimabatteries/1213/4333/7097/Battery_User_Guide.pdf
     
    #2 jb in NE, Jun 14, 2019
  3. bisco

    bisco cookie crumbler

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    do you drive much? if not, put a charger/maintainer on it and see how it holds up.

    otherwise you'll have to drive for a long time to see if the voltage comes up at all.

    11.5 is definitely low.
     
    #3 bisco, Jun 14, 2019
    Skibob likes this.
  4. sam spade 2

    sam spade 2 Senior Member

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    Yes, most likely.
    11.5 volts indicates that it is about 80% discharged.
     
    #4 sam spade 2, Jun 14, 2019
  5. ski.dive

    ski.dive Active Member

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    I'm going to put a slow 2amp charge to the battery and see if it improves.
    Is it OK to charge the 12V from the 'jump points' in the engine bay?
     
    #5 ski.dive, Jun 14, 2019
  6. richmke

    richmke Member

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    That is where I have hooked up my maintainer, and it works fine.
     
    #6 richmke, Jun 14, 2019
  7. sam spade 2

    sam spade 2 Senior Member

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    Yes, absolutely.

    Note that some "smart" chargers need you to connect to the battery BEFORE you plug it into the wall but most models don't care.
     
    #7 sam spade 2, Jun 14, 2019
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