12V Battery Dead Again??

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by 2004PriusIgnoramus, Jan 17, 2021.

  1. 2004PriusIgnoramus

    2004PriusIgnoramus New Member

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    Hey everyone,

    I have a 2004 Prius (just in case you couldn't tell from my handle). Just bought it about a year and a half ago. This past summer, the 12-Volt battery in the trunk went dead. I was worried that it was the electric (in the front), but the guy nearby who does the super-expensive Prius batteries said it wasn't that, based on the symptoms I described.

    So I ordered a new 12-volt and installed it myself in the back, following directions on Youtube. Then it worked. Problem solved.

    Or was it? A few months passed. Everything was working fine. Then, occasionally, while driving to and from work, the Prius would refuse to turn on. I would have to get a jump from a kind coworker.

    Finally, the semester ended (I am a professor), and the thing just went kaput entirely. I did not fix it right away, because we had quarantining to do and aging parents to visit. Now, I am trying to jumpstart it again off our family car's battery.

    What do you all think? Should I order a new 12-volt? Do something else? The screen on the dash (when the car is being jumped) says I have a near-full battery. I'm not sure if that means anything. Any help would be greatly appreciated.
     
  2. sam spade 2

    sam spade 2 Senior Member

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    You need to:
    Have the battery tested, AFTER it is fully charged from an external charger.
    (Did you change the new one before installing it ??)
    Check the main battery cables for tightness and corrosion......BOTH ends of both cables.
    While it's running, get the charging voltage checked.

    Many new batteries come half charged or less. "Mail order" ones come almost dead.
    IF you did not fully charge your replacement battery AND your trips too and from work are fairly short, then you may have just ran the battery dead. A good charge might solve the problem. But your "new" battery might be half used up now too.
     
  3. rjparker

    rjparker Senior Member

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    Measure the 12v with a voltmeter. It should be at least 12v and often won't boot the system to Ready around 10.5v. Ensure there is no corrosion on either side of the negative battery cable. A jump can take five minutes to work if the 12v battery is severely discharged. The discharged battery takes time to equalize with the jump battery.

    If you are not driving it several times a week, get a four stage battery maintainer like the Battery Tender Jr ($28) to keep it charged. Occasionally these cars will have excessive off state battery drain.

    3A1F89EB-95D9-4527-9DCD-6E2A79C991D8.jpeg
     

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    #3 rjparker, Jan 17, 2021
    Last edited: Jan 17, 2021
  4. bisco

    bisco cookie crumbler

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    the icon on the dash is for the hybrid battery, not the 12v battery. you're likely not driving enough to keep the 12v charged.
    you can get a smart charger to help with that. how many miles on your car?
     
  5. 2004PriusIgnoramus

    2004PriusIgnoramus New Member

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    Thank you so much. This is super helpful! I'll let you all know how it goes!
     
  6. 2004PriusIgnoramus

    2004PriusIgnoramus New Member

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    "A jump can take five minutes to work if the 12v battery is severely discharged. The discharged battery takes time to equalize with the jump battery."

    Quick question--I jumped the car for a solid half hour yesterday, but the moment I took the jump cables off and turned off the car, it wouldn't start. Does this mean I should simply get a new 12v, or should I buy and use a voltmeter first to make sure it's dead?
     
  7. dolj

    dolj Senior Member

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    That is a definite possibility, but to put in any decent charge into what looks like a deeply discharged battery, you would have needed to leave the car in READY for a good many hours – like 12 to 20 hours. So it is not surprising that the car would not start given the circumstances.
     
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  8. 2004PriusIgnoramus

    2004PriusIgnoramus New Member

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    Thank you all for your help! I will continue to follow up with your suggestions. I jumped the car yesterday and just left it running for a while. The battery recharged and the car now seems to be working just fine. I'll be investing in that Battery Tender for sure! Anything else you all would advise to prevent this from happening again?
     
  9. 2004PriusIgnoramus

    2004PriusIgnoramus New Member

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    Thank you! Yup! You're absolutely right. I left it in "ready" for an hour or so yesterday and then drove it around the neighborhood for a while, and that seemed to do the trick.

    IF.....it measures only 12.0 with no load, then it is at least 50% discharged and might (probably) drop low enough to fail when trying to start up.
     
    #9 2004PriusIgnoramus, Jan 19, 2021
    Last edited by a moderator: Jan 19, 2021
  10. rjparker

    rjparker Senior Member

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    The easy thing to do is take the 12v battery to an auto supply and have them load test it for free. If you need one, which is likely, consider getting a Toyota OEM. This is probably all you need to do.

    A serviceable 12v battery will recover enough in 5 minutes to Ready the car while jumped. In fact, this is mentioned in the owners manual.

    Extra Information

    1. Measuring the voltage while it is being jumped is not good information as you are essentially measuring the jump battery and often the jump vehicle's charging system in parallel with your battery. All vehicles, including the Prius will read a higher charge voltage when running or while in Ready.

    2. For diagnostic purposes you have to measure your battery alone at different intervals like first thing in the morning before a start and later after it has been running and then shut down.

    3. Do not continue to Jump the car after the Prius is in Ready (eg "running"). The Prius charging system is active at all times in Ready. If you are using jumper cables from another running vehicle, you then have two different charging systems working at once. Not a short term problem but not good for longer periods.

    4. It is not necessary to run the car in Ready for long periods of time to charge a 12v battery. In fact that strategy has downsides if you done unattended, as engine or coolant problems could occur that go unnoticed. You are also unnecessarily cycling the high voltage battery hundreds of times. Bad idea. If you must charge a 12v battery get a proper charger like a Battery Tender Jr ($28) and leave it connected overnight. A charger like this is also highly recommended for use if the car is not being run for weeks at a time.

    5. If the battery is being quickly discharged while the system is off, it is often excessive parasitic current draw causing the issue. Typically a light left on because the rear hatch was not completely closed or a maplight that was left on turns out to be the root cause. However there are other sources that require a trained auto electric technician to track down. There are relatively easy techiques to measure the symptoms using a voltmeter or to actually measure the parasitic draw with an advanced use of the meter. The amp modes require series connection of the meter, not the typical parallel voltage reading modes.

    A voltmeter should be in your tool box and a serviceable one can be had for a very low investment. Knowing how to use it can be another issue.
     
    #10 rjparker, Jan 19, 2021
    Last edited: Jan 19, 2021
  11. Skibob

    Skibob Senior Member

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    How long time wise is your average drive and how many times a week are you driving?
     
  12. 2004PriusIgnoramus

    2004PriusIgnoramus New Member

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    So here's an update--after having numerous other battery problems and having the 12v charged at Advanced Auto, it stopped working altogether. I finally just gave up and had it towed to the Dealership. They said the problem is that the battery has a dead cell and that the coolant hose is leaking. I may just have it towed back to my house, as the battery I bought this summer is still under warranty and the dealer (naturally) wants to take all my money. Is the coolant hose something that an ordinary auto shop can repair?
     
  13. edthefox5

    edthefox5 Senior Member

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    Pretty common story Professor.

    Once that little battery gets completely discharged especially discharged deeply and perfectly by leaving a light on it will never be the same IMHO.
    It will never take a full charge again. Especially if its sits for a while stone dead and held dead by a light bulb.

    You never posted the mileage on the car.

    You must arm the cars alarm every time you walk away from the car it will not arm if you left a door ajar.

    I always without exception before i go to bed I will go out front and look at my cars make sure there locked and I didn't leave a light on.
    Check the car in the garage too.
    It has stood me very well I have never had to go through what you just went through.
    Old Cars are a pain in the nice person you have to stay on top of them or they will stay on top of you.

    I check the battery voltage on my 07 prius at least once a month with my digital voltmeter at the front jump point. Never check at the battery always check at the front jump point. Do not go into the hatch.

    A healthy driven well Prius battery lives at 12.6 volts at the front jump.
    Anything less then that it goes on my sh*t list and i start watching and testing it..

    My just 3 years and 3 months old on a 3 year warranty Yellowtop just started going from 12.6 to now 12.3. And is now unable to light the full green light on my charger.

    Ok I know for sure its new battery time. Only a matter of time. Going with a Batteries+ Duracell nice 4 year warranty SB model drop in. No more yellowtops.


    .
     
  14. rjparker

    rjparker Senior Member

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    Yes any shop can change a hose. You may want to check with your battery supplier and find out how much a new battery will cost after it is prorated. If it is a half or more of the new price you might come out ahead by getting the Toyota battery at the dealer and avoid the tow cost. Don't be afraid to negotiate with them.

    Finally, don't allow a battery to sit for weeks or longer on a regular basis. Use the four stage charger or simply drive it for thirty minutes once a week. Your tires, brakes, engine, suspension and electrical systems will benefit. Plus you don't want a year old stale tank of gas.
     
  15. edthefox5

    edthefox5 Senior Member

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    Batteries+. Plus Duracell is $226.
     
  16. 2004PriusIgnoramus

    2004PriusIgnoramus New Member

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    Much obliged! Thanks for the advice!
     
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  17. 2004PriusIgnoramus

    2004PriusIgnoramus New Member

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    Thanks so much! Because I bought my battery in July, it was still under warranty. With some arm-twisting (and a lot of driving around), I got the Advanced auto guys to take back the old battery and give me a new one. The Dealer says they will install it for $90, which is fine by me, as it saves the cost of towing.
     
  18. edthefox5

    edthefox5 Senior Member

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