12v Battery Is Discharging, Re-Charge Now !

Discussion in 'Prime Care, Maintenance and Troubleshooting' started by Rob43, Apr 18, 2020.

  1. Salamander_King

    Salamander_King Senior Member

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    While I was checking my PRIME's less than 1 year old 12v battery, I also checked our two other car batteries. Both cars are hybrid and 12v is not used for starting engine, I think. One is OEM Nissan battery at least 6 years old, other is aftermarket EXIDE battery less than 3 years old. All three batteries including my PRIME's OEM battery showed 12.42v-12.47v on battery tester reading with 70-78% health initially. At least on my battery tester, anything above 12.4v seems to be fine.
     
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  2. Salamander_King

    Salamander_King Senior Member

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    Day 2. After 36 hours, the battery is now 12.74v, but still 100%. In 24 hours period, it discharged 0.15v. If the discharge rate is constant, then after 7days, the projected losses will total 1.05v. Starting from the full charge of 13.06v, it will be down to 12.01v or 50% in one week.

    Screenshot 2020-04-21 at 6.50.33 AM.png
     
    #22 Salamander_King, Apr 21, 2020
    Last edited: Apr 21, 2020
  3. bisco

    bisco cookie crumbler

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    wow, if this is typical, toyota has really dropped the ball on 12v battery management. after 15 years of 12v problems, i can't believe they've made it even worse. especially after moving the battery to the engine compartment, where they coud have installed a beefier unit.
     
  4. Salamander_King

    Salamander_King Senior Member

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    Is the flooded acid battery self-discharge rate affected by temperature? It was low 20s this morning.
     
  5. Trollbait

    Trollbait It's a D&D thing

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    Yes, it will be faster at higher temps.
     
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  6. Salamander_King

    Salamander_King Senior Member

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    OK, that means in my local self-discharge is already lower than hotter places.
     
  7. Rob43

    Rob43 Senior Member

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    So far I'm not concerned about your 2020 ~new 12v battery based on everything you've posted. I normally expect a battery of this nature to fall back to ~12.7 / ~12.6 volts and then stabilize there. So your next ~6 days of reporting might be very interesting.

    **************************************

    Now think about all of this "12v Battery Is Discharging" stuff from the average persons point of view.

    The average person did not re-charge their Prius Prime the day before it sat for 1, 2, 3, or 4 weeks. The average Prime owner "probably*" was sitting on roughly a ~12.4v battery charge (~75%) and then the chassis just sat day after day until the day it would not start up...


    Rob43

    * "Probably" is derived from all of the countless times I've personally checked my Primes 12v battery with my volt meter and come up with an average of roughly ~12.35 / 12.4 volts.
     
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  8. bisco

    bisco cookie crumbler

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    i'm surprised we haven't seen more complaints. there have been tons of gen2 and 3 covid 12 volts
     
  9. Salamander_King

    Salamander_King Senior Member

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    After 1 week, I will see what 30 miles drive will do to the battery. That's what I have been doing last 4 weeks, and I did not have problem.
     
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  10. Rob43

    Rob43 Senior Member

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    Does anyone know the approximate low voltage tipping point of the 12v battery not working / not able to start the Prime ?


    Rob43
     
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  11. Salamander_King

    Salamander_King Senior Member

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    I don't know the answer. But since it dose not need to crank the engine, I would think it can be lower than regular car.
     
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  12. Salamander_King

    Salamander_King Senior Member

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    Here is reading 52 hours after a full charge. It is now reading 12.72v. In the last 24 hours, the discharge was from 12.81v to 12.72v, a total of 0.09v.

    Screenshot 2020-04-21 at 11.58.56 PM.png
     
  13. benagi

    benagi Active Member

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    I remember on our Prius V, when the battery died, it was in the low 10 V range that would not start the car. Though I did get five years out of the12 V battery.
     
  14. Rob43

    Rob43 Senior Member

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    On the surface, this doesn't seem like a big deal...

    But let's round up and call it 0.10 volts lost per 24 hour day, now it's just a matter of time before there's not enough voltage to make the computer wake up & start the car.

    There also is the possibility that your much newer 2020 Prime 12v battery losses a bit less per day over time, but my older Prime might lose even more per day based on age. Then it just becomes a quicker matter of time for the slightly older chassis.


    Rob43
     
    #34 Rob43, Apr 22, 2020
    Last edited: Apr 22, 2020
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  15. Salamander_King

    Salamander_King Senior Member

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    Agreed. My Primes almost brand new battery that was only driven for two weeks after purchase on March 1st and driven only once a week ~30 miles after mid-March was measuring 12.38v before the full charge. If it did lose 0.1v each day, after a week, it could go down to ~11.7v which is still OK charge for starting PRIME, but if it goes longer periods, say a few months, it may not hold enough charge to start the car.
     
  16. bisco

    bisco cookie crumbler

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    from past history, the resting voltage is not a good indicator of a weak battery. it seems that the voltage under load can vary, battery to battery with the same resting voltage. and that's what makes testing tricky.

    in older cars, there also seems to be an element of the cars internals also varying from car to car, putting more or less load on the batteries.
     
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  17. thymara

    thymara Junior Member

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    Today my 2020 Prius Prime was @ 12.24 with a multimeter. This thread has inspired me to check on a regular basis. Even though I've had the vehicle since end of Jan I've only travelled 300 KM, difficult to go anywhere given the virus conditions. Spreadsheet initiated.
     
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  18. bisco

    bisco cookie crumbler

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  19. Hicksite

    Hicksite Junior Member

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    Looking at CTEK, Nocco, and Battery Tender chargers. Any recommendations?
     
  20. Trollbait

    Trollbait It's a D&D thing

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    Yeah, but electronics can be picky about electricity 'quality'.

    Also climate has an effect. Along with how long the car sat on the dealer's back lot.
     
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