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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    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
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  2. ChapmanF

    ChapmanF Senior Member

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    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
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  3. rjparker

    rjparker Tu Humilde Sirviente

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    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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  4. Mendel Leisk

    Mendel Leisk MMX GEN III

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    Yeah, that's an "ex" battery.

     
    #4 Mendel Leisk, May 30, 2026 at 11:45 AM
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  5. notspam3

    notspam3 Member

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    LOL this must be the first vehicle you have ever owned.

    I was happy my 2013 Prius V 12V battery lasted 12 years. Normally lead acid car batteries are good for 5-8 years. Anything over 8 years is a bonus.
     
    #5 notspam3, May 30, 2026 at 12:55 PM
  6. bisco

    bisco cookie crumbler

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    my wife had the same thoughts years ago when her dog 'just died' in the back hall. she'd never heard of such a thing.
    the trickle charger was useless...
     
    #6 bisco, May 30, 2026 at 1:24 PM
  7. Dave Jeffries

    Dave Jeffries Junior Member

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    So true and that is the case for me!
     
    #7 Dave Jeffries, May 30, 2026 at 2:36 PM
  8. Dave Jeffries

    Dave Jeffries Junior Member

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    Hardly. I have been the proud owner of a vehicle since Feb 1968. Not too bright of me eh?
    My 2016 F150 is on the same battery it came with. I regularly do a recondition on it with my CTEK charger and when it sits, I connect a trickle charger. A bought a new battery for the Prius today.
     
    #8 Dave Jeffries, May 30, 2026 at 2:44 PM
  9. Dave Jeffries

    Dave Jeffries Junior Member

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    Thanks for the comments.
    I left the CTEK charger on the battery 15 hours. When I looked at it this morning, it was in recondition. I considered this a sign that the battery was toast. I sure wasn't going to trust it anymore. After replacing the battery and connecting a pigtail to the battery so I don't have to tear the car apart to charge the battery, I noticed that the driver courtesy light was one. Don't know for sure, BUTT this could be the cause of the battery being drained. Hope so. Time will tell.
     
    #9 Dave Jeffries, May 30, 2026 at 2:52 PM
  10. Mendel Leisk

    Mendel Leisk MMX GEN III

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    Dedicated, 12 volt, battery testers can check it's viability; prosumer level ones are $50 and up, pricey ones with a built-in printer (which is not really necessary for DIY). Solar BA9 is what I'd get if shopping now.
     
    #10 Mendel Leisk, May 30, 2026 at 6:21 PM
  11. BiomedO1

    BiomedO1 Senior Member

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    ALL newer ECU controlled cars especially with keyless entry and keyless ignition will draw more power than the old school ICE cars. The old school ICE cars closes a relay and the only battery draw is maybe a clock and/or alarm. Modern car will always draw power to scan for a fob and keep ECU parameters alive.

    The only way to figure out if you have a parasitic draw; is to test it. I believe it should draw < 50mA when everything goes into sleep mode. Double-check the manual to make sure that number is correct.

    FWIW; that 14+V you got with the car running was the DC-DC converter pumping voltage back into your battery - IT WAS NOT your battery voltage. That test only tells you if your charging system is working. ie. if you have a bad alternator on an old school car; which should trigger your battery lamp.

    Good Luck.......
     
    #11 BiomedO1, May 30, 2026 at 6:55 PM
    Last edited: May 30, 2026 at 7:01 PM
  12. rjparker

    rjparker Tu Humilde Sirviente

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    #12 rjparker, May 30, 2026 at 6:56 PM
    Last edited: May 30, 2026 at 8:54 PM
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