12v Battery Is Discharging, Re-Charge Now !

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

  1. thymara

    thymara Junior Member

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    I have been using 12.4V as the magic number, mostly driven by comments in this and other threads about the importance of 12.4. I acquired the vehicle late January, 2020, hardly drove it but had no issues starting it and I was not using the battery tender. Maybe all the posts talking about this issue have made my paranoid. On a number of occasions this summer while on vacation, and not using the vehicle, there have been no issues over 2 week periods.

    Winter tires go on this Thursday.
     
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  2. Salamander_King

    Salamander_King Senior Member

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    I have similarly new 2020 PP that I purchased at the end of Feb this year that have not been driven much. Yeah, I think I agree with you about the "paranoid" part. Reading stories of others reporting a dead 12v battery and needing to replace with a new one when the car is less than 3 years old has made me to worry about it, but @vvillovv maybe correct that the charge above 12v would be just fine for PP. Then again, since I am not driving the car much, I have nothing else to do with the car. Monitoring and tendering the 12v battery gives me something to do with the car everyday. It's more of the hobby and daily routine at this point.

    For my previous cars including 2017PP and 2015Gen3, I never paid any attention to the 12v battery charge. I never had any issue for the first 3 years for Gen3 or 2017 PP after the purchase. But that was with daily use. Car was driven average of 40miles/day or 15Kmiles/yr, and never sat idle for longer than a few days at most. In my past experience, only time I had problem with the 12v battery was on ICE vehicles during the coldest months of winter morning when the engine will not turn over. But the 12v battery was usually well over 5 years old by then. A quick charge with a "dumb charger" revived the 12v battery, and can be driven for a while until I had chance to run to a local auto supply store to pick up the replacement battery at about ~$100. It was easy and cheap DIY maintenance thing.

    The only hybrid car with a dead 12v battery experience I had was my HCH after the traction battery started not to hold charge. On HCH, just like Prius, the traction battery starts the engine normally, but unlike Prius, if the traction battery SoC gets very low, the 12v battery will take over the start-up engine cranking duty. The dying traction battery consequently resulted in the dead 12v battery on my HCH, but this happened at 9 years and 6 mo mark with 142K miles on the car. Both the traction and the 12v battery were original. BTW, I had to purchase and DIY install the 12v battery before the IMA traction battery finally died. The DIY aftermarket 12v battery replacement costed me ~$100 but the dealer replacement of the traction battery costed me nothing due to battery warranty still in effect.

    I think if the car is driven on daily bases, then the 12v battery charge below 12.4v is probably fine in our PP. The question is under COVID-19 restriction, if the car is not driven regularly, would it shorten the life span of the 12v battery if one let the voltage to drop below 12.4v and don't charge it up? I don't have an answer for you. But I am not going to press my luck, since I have already invested in the 12v battery monitoring and charging equipment. At this point it's cheaper to maintain the 12v battery charged and healthy as the voltage drops below 12.4v than to let the 12v battery drain and strain and needing to have to replace it sooner than usual.

    upload_2020-10-19_9-1-39.png
     
    #342 Salamander_King, Oct 19, 2020
    Last edited: Oct 19, 2020
  3. bisco

    bisco cookie crumbler

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    i thought 12.4 was the magic number, until the day it read 4.4 after reading 12.4 the day before.

    load testing is everything.
     
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  4. vvillovv

    vvillovv Senior Member

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    I wouldn't say I know why Rob43 started this thread, although I was interested in it the first time I read his OP.
    I've done the de-sulfate thing on two 12 v flooded lead acid batteries and one lasted 2 more years in the car with float charging in the colder months and the other never fully recovered and was replaced. So it all depends. pretty much like everything else.
    I was amazed at some of the 12 volt readings I got at different times during the Primes operation.
    I read that Rob43 said in one of his earlier posts in this thread that he also doesn't know how the Primes electrical system works - paraphrasing.
    The more data we can gather here about when the Prime charges the 12 volt and when the Prime uses the 12 volt will help to dispel some of the myths and transients involved with diagnosis.
     
  5. Qmo

    Qmo Member

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    Well, only to find this page after having trouble starting my 2017 Prime. :(
    it was 28F earlier so hopefully, it's due to the cold weather and maybe I can still recharge it? :(
    Am still waiting for GEICO's roadside assist after 2 hours....
     
  6. bisco

    bisco cookie crumbler

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    you can invest in a smart charger and take a chance, or a new battery. the charger might come in handy, even if the battery is toast. it's a tough call on a 4 year old battery. for some, that's the life expectancy, for others, it's half.
     
  7. Qmo

    Qmo Member

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    Does anyone know the battery type in a 2017 PP?
    Just received my Noco Genius5 but can't tell from the label on the battery and am not sure if I should select 12V, 12V AGM or 12V Litium.
    Thanks.
     
  8. Salamander_King

    Salamander_King Senior Member

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    It is just a regular flooded lead-acid 12v battery. On a smart charger, it is usually a default setting. If the selection lists are those three "12V, 12V AGM or 12V Lithium" then "12V" would be the one to use.
     
    #348 Salamander_King, Dec 12, 2020
    Last edited: Dec 12, 2020
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  9. Qmo

    Qmo Member

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  10. Storm88000

    Storm88000 Member

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    So today I got a message in the upper screen that the battery was low (2020 Prime). I was talking on the phone w/ CarPlay with the accessories on for an hour in a parking lot so perhaps it’s my fault (likely is) - here’s the oddest part:

    I had less than 2.0 miles of all electric driving left when I shut the car off. After that screen came up about the battery being low, and I got it started up again, I suddenly had 19.0 electric miles? Not an error on the screen because I drove home worried something was wrong and it used the 19.0 miles down in around how long 19.0 miles would last.

    Anyone have an explanation for this? So weird.
     
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  11. Sandy Mc

    Sandy Mc New Member

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    I have a 2020 Prius Prime, it was used when I bought it with only 3,000 miles. The first 4 months the main battery would charge up to 33 miles. Since Dec. the battery started lowering to only 30 mile charge and now only 27 miles. I took it to a Toyota dealer and they said that was normal during the winter. My car is in a garage all the time and the temperature is never below 40 degrees. What I'm wondering is if this is a faulty battery and if they just don't want to replace it? I don't want the charge to continue dropping so that eventually I may not get a charge of battery at all. It's still under full warranty so I don't understand. Anyone else had this problem with their Prime?
     
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  12. Dael

    Dael Member

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    this is normal, they quote the range of battery @25 so. when I first got mine (sept. 2019) it wouldn't go above 25, finally when things warmed up it got up to 32. now that winter is here again it's back to 26. my garage hovers between 40 and 50.
     
  13. Salamander_King

    Salamander_King Senior Member

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    Welcome to PC. As said above, what you are seeing is perfectly normal seasonal variation. Remember the miles displayed on the dash are just an estimate of EV range, not the indication of battery health. The car estimates this from your recent drives on EV mode and other factors that affect EV range such as temperature. During the winter colder climate, the car uses more energy on heating and the battery is not as efficient in colder temperature. You will see a drop in EV range due to loss of efficiency which you can find out in Eco Diary. I usually saw 32-35miles of EV range estimation on the dash in summer which corresponds to 5-6miles/kWh efficiency but that dropped 22-25miles during winter corresponding to 3-4miles/kWh. This is not related to battery degradation and you should not worry about it.

    OTOH, the battery degradation does happen over time regardless of you charging the battery during winter or not. From what has been reported this normal degradation is relatively small for the most part (1-2%/year in some reported cases). To prevent degradation, Toyota recommends not to keep the cattery charged fully when not being used for a long time. If you are driving your car every day, then using the charge schedule to minimize the time the battery sit fully charged is the best practice you can use. Otherwise, just enjoy the drive.
     
    #353 Salamander_King, Jan 15, 2021
    Last edited: Jan 15, 2021
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  14. bisco

    bisco cookie crumbler

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    yes, is not a problem houston
     
  15. srivenkat

    srivenkat Active Member

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    ONE WAY TO KEEP THE 12V BATTERY CHARGED UP, if the Prime isn't being driven much, is by switching on the Prime and leaving it on (READY mode) with sufficient charge in the Hybrid/EV battery to last the charge session. But the Prime automatically switches off, if the car isn't driven within some time of switching on the car. But as noted by others (augmented with my experience in the below post), the auto-switch-off can be gotten around by locking the doors using the metal key in the keyfob (can't lock the doors with the keyfob buttons while the car is in READY mode, hence the metal key needs to be taken out of the keyfob and inserted into the door handle and turned counter-clockwise to lock the doors) and then the car continues to remain in READY mode without automatically shutting off.

    The traction battery is ideally charged up enough to not bring the engine on during the above 12V charge session. Also, a most important commonsense SAFETY PRECAUTION would be to leave the garage doors open in case the hybrid battery charge gets depleted before the car is manually turned off at the end of the above charge session and the engine comes on to charge the HV battery. Also, I would switch off all the accessories, including seat heaters and the display also (on the XLE go to Home->settings->Display off) during the charge session so the EV battery charge lasts long enough.

    #6
     
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  16. Salamander_King

    Salamander_King Senior Member

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    Yap, I have shown it on my comment linked below. Total ~4 hours in READY mostly parked charged up the 12v battery from 12.47v to 12.92v.
    12v Battery Is Discharging, Re-Charge Now ! | Page 15 | PriusChat

    However, an interesting observation is that driving the car for 4+ hours did not charge the 12v battery as much as just keeping the car in READY and parked. Read my comment here: 12v Battery Is Discharging, Re-Charge Now ! | Page 17 | PriusChat
     
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  17. dbstoo

    dbstoo Active Member

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    The difference you are seeing is due to the car learning how YOU use it. When the car is brand new (or when 12v battery is replaced), it estimates the miles available based on a theoretical "best case" scenario: eco setting, light foot and climate control off. As you drive it, the car learns that you don't coast much, and that you use the A/C and heater a lot.

    The next time it charges, turn off the climate control after putting it in "ready" in and watch the "miles" change.

    I have experienced a few interesting situations where I left the house with 27.5 miles available for a 2.2 mile round trip to the store. Due to the geography of the trip, I got home with 27.2 miles available. I drove it gently in eco mode, caught all the lights (both ways) and coasted where appropriate. The next day after charging the display showed that I had 28+ miles available. :)

    Dan
     
  18. Mark in NY

    Mark in NY Junior Member

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    I recently discovered this issue when I measured 11.6 vdc at the battery one morning before driving the car. It was driven just a few days before. Snapon battery analyzer says battery has 76% capacity. Mechanic says they change them when the analyzer shows 60-65% capacity so it seems a replacement battery is not immediate but not too far away. I have owned the car for 3 years.
    I am investigating an Ohmmu lithium replacement battery but that is on another thread. More to your point - the prime manual says during extended parking / non-use the car will go into hibernation mode and shut down normal computer operation to conserve battery energy. At that point you have to use the metal key to get into the car but it should then start normally. During online searching of replacement battery options I found that Tesla owners have 12 volt battery short lifespan issues and there is a fair amount of interest in lithium replacement batteries for those cars.
     
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  19. PiPLosAngeles

    PiPLosAngeles Senior Member

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    That's because when you put the car into drive the DC-DC converter voltage drops from ~13.8 to ~12V.

    I'd be leery of using a lithium battery in an engine compartment because of high temperatures, which degrade lithium batteries rapidly.
     
  20. Salamander_King

    Salamander_King Senior Member

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    Yap, the voltage of the 12v battery at the terminal drops as soon as the car goes into DRIVE, and kicks up above 13v occasionally, where as in READY mode parked car shows at ~13.8v all the time. That's what the graph shows. 12v Battery Is Discharging, Re-Charge Now ! | Page 17 | PriusChat
     
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