Dashboard Msg: Aux Battery Low

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Starbrand, Nov 23, 2018.

  1. Starbrand

    Starbrand Senior Member

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    I got this message on a 2015 prius. Happened only twice within 2 weeks. Car has trouble booting up, but was fine after 5 mins, then started.

    What are the main issues and the best way to fix?
     

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  2. sam spade 2

    sam spade 2 Senior Member

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    Two common causes:
    Loose main battery cables.
    12 V battery going bad.

    Get the battery tested and the connections checked.
    Likely you will need a new battery but that's a bit unusual after only 3 years.
     
  3. bisco

    bisco cookie crumbler

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    interesting message, i didn't know there was a 12v warning on gen3.

    get an agm compatible trickle charger and charge it up. if it won't hold, replace it.

    check with your dealer about warranty
     
  4. FuelMiser

    FuelMiser Senior Member

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    A 3 to 4 year old battery should not have problems holding a charge, but you could have it checked at an auto parts store or battery store for its ability to hold a charge. One reason it could be running down is you have something plugged-in to a USB port or OBD port while the car is off. The 12V battery is very small, so it runs down easily in the Prius. Something like this (pic) could show you the battery state without accessing the actual battery terminals. If you press the Power button without pushing the brake pedal first, you will see the level in the battery alone. It should be above 12.0 volts. Then after the car is in Ready state, you will see the level of the charging system. This should be above 14.0 volts.
     

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  5. sam spade 2

    sam spade 2 Senior Member

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    I think you KNOW not to recommend a "trickle" charger for anything.
    Old habit are hard to break ??
     
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  6. sam spade 2

    sam spade 2 Senior Member

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    Good point. I was thinking about not getting a door fully closed so that the dome lights stay ON......but those are supposed to "time out" on most/all models. Leaving a "map light" on too.
     
  7. Bill Norton

    Bill Norton Senior Member

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    Why do you say this??? Just curious...(n)

    I think my AGM 2 amp 'minder' with an 'anti-sulfation' function has extended the life of EVERY Lead Acid battery I own.

    I have a +4 yr, $30, lawn mower battery. Top that !
    And I had my Prius LA battery on it for 3 days,
    But I had it disconnected to make sure the AC pulses were absorbed only by the battery.
     
  8. sam spade 2

    sam spade 2 Senior Member

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    That unit is NOT a "trickle charger".
    It is an automatic battery maintainer.

    A "trickle charger" implies no controls at all and typically when the battery nears full charge the voltage goes ABOVE the recommended float value. That tends to electrolyze the water and will ruin the battery over a long term.

    Recommending that people use a "trickle charger" is NOT good advice........unless maybe they will only connect it for a day or two each month.
     
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  9. bisco

    bisco cookie crumbler

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    idk, if you google agm trickle charger, you get a lot of smart chargers and maintainers. some call themselves trickle chargers, some don't. semantics i suppose
     
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  10. sam spade 2

    sam spade 2 Senior Member

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    No it is NOT just semantics.
    There is an important difference.

    A trickle charger is NOT automatic and requires some manual intervention.

    Anything that calls itself a "trickle charger" should be avoided if you want unattended service.
     
  11. padroo

    padroo Senior Member

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    Warning, read the directions that come with your " trickle charger ".
     
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