12v Battery Is Discharging, Re-Charge Now !

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

  1. Rob43

    Rob43 Senior Member

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    This is what I've got, after a total of ~19 hours of sitting my 12v battery voltage on my voltmeter was 12.07 volts. The Prime was then started up and driven away.

    Here's how I look at this at this point:

    Salamander_King's 12v battery is very new and currently it's surviving this testing quite well.
    My Prime 12v battery is probably much closer to the "average" 12v Prime battery that most of us are driving around on, it has gone through this roller coaster of up & down voltage for a while now & it is not doing as well.

    Based on my ending voltage of 12.07 volts today, I'm confident that if I parked my Prime like many of us that within ~2 weeks I'd walk out to a dead Prius Prime.


    Rob43
     
    #121 Rob43, Apr 25, 2020
    Last edited: Apr 25, 2020
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  2. Salamander_King

    Salamander_King Senior Member

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    Here is my reading of 12v battery on today's ~50 miles drive. I run a few errands along with my weekly work-related drive.

    1) 2020-04-19 20:23 13.06v. 12v fully charged. No opening of door or fob near the car during this time.
    2) 2020-04-25 11:37 12.58v From 13.06v right after fully charged the battery drained down to 12.58v in 6 days.
    3) 2020-04-25 11:55 12.24v In preparation for the trip. I had to keep the hatch door open for ~17min. After opening the driver side door the 12v reading dropped as low as 12.24v before starting the car.
    4) 2020-04-25 11:55-12:58 14.42v During 32 miles trip (1 hour) the 12v was being charged at constant ~14v. The charging started as soon as I started the car.
    5) 12:58-14:11 12.69v low at PARK. I had two additional stops I made and drove ~18 miles. When car was parked 12v dropped to as low as 12.69v, but as soon as the car is started it gets charged at ~14v, but after a while, the charge voltage dropped to ~13v for floating charge most of the way back home.
    6) 14:13 12.69v After reaching home and turning off the car and getting out of the car, 12v reading dropped to the 99% 12.69v.
    7) 14:31-16:17 12.81v-12.78v After the car was turned off, in the next 18 min the battery charge came up and stabilized at ~12.8v 100%.

    It looks like the brand new 12v battery in PRIME after fully charged keeps the SOC above 90% 12.56v during 6 days PARK without disturbance. And ~1 hour of driving is sufficient to bring it back to a full charge again. My current schedule should be enough to keep the battery in good shape, as long as I do not open the door and use 12v during PARK.

    I will plug in L1 EVSE later to top off the traction battery to SOC level 35-45%. I will check what happens to 12v during hybrid battery plug-in, but I don't think it will add much charge to already 100% 12v battery.

    Screenshot 2020-04-25 at 4.25.53 PM.png
     
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  3. Rob43

    Rob43 Senior Member

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    When my Prime returned today from its quick trip:

    While it was still ON it showed 13.67 volts, I then turned it OFF and it measured 12.33 volts. I will now charge the traction battery up with my L2 EVSE and check the 12v battery voltage when the traction battery charging is at about 90% and still going.



    Rob43
     
  4. bisco

    bisco cookie crumbler

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    so after a week, has anyone been able to let the car sit and get 7 readings on the battery?
     
  5. Salamander_King

    Salamander_King Senior Member

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    7 readings?
     
  6. bisco

    bisco cookie crumbler

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    one each day since 04-18?
     
  7. Rob43

    Rob43 Senior Member

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    So when the traction battery was charged to roughly 90% and still charging, I took a 12v battery reading of 12.80 volts. Once the traction battery was finished charging I unplugged the EVSE charge handle and closed the access door. After about ~15 minutes I came back and measured 12.43 volts.


    Rob43
     
  8. bisco

    bisco cookie crumbler

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    so that difference is the surface charge?
     
  9. Salamander_King

    Salamander_King Senior Member

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    I started my test on 04-19 (Sun).

    4-19 12.56v before charging 13.06v after fully charged
    4-20 12.87v
    4-21 12.74v
    4-22 12.67v
    4-23 12.61v
    4-24 12.57v
    4-25 12.56v drove ~50 miles, aux batt back to 12.75v

    2 hours after the car was parked, the AUX battery was still 12.75v. I plugged in L1 to my car for ~2.5 hours 2.88khw up to SOC43%. When L1 is plugged in, the AUX bat reading went up to 13.31v immediately and the AUX bat was charged briefly. But it stopped very quickly, less than a minute. The AUX battery stayed ~12.7v during plug-in and after. I am going to let the car sit another week.

    Screenshot 2020-04-25 at 8.27.33 PM.png
     
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  10. bisco

    bisco cookie crumbler

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    i suppose a battery isn't linear? is that why the drop gets smaller each day?
     
  11. Salamander_King

    Salamander_King Senior Member

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    Yeah, that was the case with mine. Mine did stabilize at around 12.56v.
     
  12. Mendel Leisk

    Mendel Leisk Senior Member

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    Or it's currently somewhat stable around 12.56? Continuing to have protracted downtime without charging, I'd speculate that stable point will slowly drop.
     
  13. Salamander_King

    Salamander_King Senior Member

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    Isn't it the natural degradation of capacity for any battery? My almost brand new 12v battery seems to have stabilizing capacity at 12.56v, but Rob's 3 years old battery has much lower capacity at resting state due to natural degradation?
     
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  14. Hicksite

    Hicksite Member

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    Differences in temperatures could also be a factor in the amount of the drop right? Or was the temperature pretty much the same each day? But anyway I suspect the discharge rate wouldn't be 100% linear, even for a resting battery under laboratory conditions!
     
  15. Salamander_King

    Salamander_King Senior Member

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    Yes, my 24-hour monitoring of 12v battery reveals the lowest SOC is at early morning day low temp and then SOC actually goes up a bit during the day and highest at day high in the afternoon.

    According to @Trollbait the amount of self-discharge is higher at higher temperatures. I believe that is due to the battery chemistry. But in my climate around this time of year, daytime high of 45 and low of 25 seems to favor the higher temp for more SOC in the 12v. But YMMV.

    As for the effect of the temperature on the battery life, it is known that the higher ambient temperature shortens the battery lifespan. In my region, average 12v battery life is estimated to be 5 years, but I have never had any 12v battery fail in less than 6 years in our cars in the past. I had several OEM batteries that lasted over 10 years before dying. This without any precautionary maintenance.

    Screenshot 2020-04-26 at 10.35.08 AM.png
     
    #135 Salamander_King, Apr 26, 2020
    Last edited: Apr 26, 2020
  16. Mendel Leisk

    Mendel Leisk Senior Member

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    The demarcations on that map should maybe dip in the middle, climb at the two coasts? More so on the west coast, since the eastern seaboard seems to experience tougher winters? Anyhoo...
     
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  17. Salamander_King

    Salamander_King Senior Member

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    Yeah, that was the first image on Google search. Is this one better? ;)

    Batteries Etc. - Home
    Screenshot 2020-04-26 at 10.41.23 AM.png
     
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  18. Mendel Leisk

    Mendel Leisk Senior Member

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    Mmmm, okay.



    :ROFLMAO:
     
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  19. Rob43

    Rob43 Senior Member

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    OK, 24 hours later my 12.43 volts dropped down to 12.08 volts, my Prime has not been touched during this time. Unfortunately I was forced to open my Prime right after taking this reading because I needed to get something out of it, I'm going to call this computer activation with dome lights on (~40 seconds) ~24 hours worth of 12v battery usage. My Prime will get driven off Monday AM, at which time I will take a 12v reading before it starts up and drives off. I'm betting we'll see a voltage of Less than 12 volts Monday morning...


    Rob43
     
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  20. Hicksite

    Hicksite Member

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    It will be interesting to see if it starts at under 12v.
     
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