Battery Totally Discharged, Why?

Discussion in 'Prius v Care, Maintenance and Troubleshooting' started by Dave Jeffries, May 29, 2026 at 11:35 PM.

  1. Dave Jeffries

    Dave Jeffries Junior Member

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    Location:
    Vancouver, WA
    Vehicle:
    2005 Prius
    Model:
    II
    12V seemed completely discharged. I put a pigtail on to connect my charger to the battery and have the pigtail available to attach a trickle charger later. When I undid the bolt fasting the negative to the body there were no sparks. I have had the charger on for about 3 hours. The CTEK charger is still in the first phase. The voltage at the battery was 5..5v. There was a noise coming from under the hood, driver's side by the firewall. I got another battery and jumped the car. I started the engine and let it run for awhile. Was getting 14+ at the battery with the engine running. After turning off the engine, the noise(pump) I was hearing before stopped.

    This is a 2013 Prius V with most likely, the original battery. I have never had a battery just die. Usually there is a voltage drain somewhere.

    Car was last driven two (2) days ago. This morning the 12V battery was dead! Wife called while I was at work in a crawl space so I wasn't about the jump up and see if I could do something.

    Also, there is a flashing red light in the lower right of the dash of a car with a lock. Have no idea what this means. It did go out when I started the car and returned when I turned the car off.

    I should replace the battery in any case and hope there is not a low voltage leak that is causing this issue.
     
    #1 Dave Jeffries, May 29, 2026 at 11:35 PM
  2. ChapmanF

    ChapmanF Senior Member

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    Location:
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    Vehicle:
    2010 Prius
    Model:
    IV
    At least one of those questions I can answer.

    That's the "security indicator", which "flashes after the 'POWER' switch has been turned off to indicate that the system is operating" according to the owners' manual.

    It's completely traditional for people never to notice that in the whole time they've had the car, and then suddenly notice it when paying attention for some reason (like after a discharged battery), and then feel convinced it's something new they never saw before.

    So, welcome to the club. :) (y)
     
    #2 ChapmanF, May 29, 2026 at 11:44 PM
  3. rjparker

    rjparker Tu Humilde Sirviente

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    Texas Hill Country
    Vehicle:
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    Model:
    Three
    5.5v means the battery had a heart attack and died. Typically a bad internal connection. It happens. No 12v starter to give you an early warning.

    In dog years an original 2013 battery lasted twice its normal lifespan.

    You can do a parasitic draw test with an ammeter in series with the negative battery terminal. 98% it will be a waste of time.
     
    #3 rjparker, May 30, 2026 at 12:47 AM
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