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What keeps killing my battery ?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by 1prius, May 10, 2019.

  1. 1prius

    1prius Junior Member

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    Hey all - Noob to this forum - but been wrenching on cars for ever.

    This is the third time in as many years that my battery just up and died. The car is driven most every day and everything seems to be doing fine. Yet out of the blue - dead battery. This last battery wasn't even a year old.

    What ever it is draining it, it was bad. This time I put a smart charger on it and it only had 4.9 volts. Let the charger run about half an hour and checked it. The charger was flashing it was a bad battery. Reset it and after another half hour, it had come up to 6 volts but the charger was once again flashing bad battery.

    So I disconnected the + cable and in 30 minutes it was up to 12 volts but only 60% capacity.
    The car would now start but the battery was toast and wouldn't take any more charge.

    That's a big difference! What ever was causing the drain was still happening until I disconnected the cable. Also the HV battery was drained down to only two bars but when it was parked it was at 5 bars. I know the HV battery is getting tired as it rarely takes a full charge anymore. But that should not affect the 12v battery system.

    Next morning the car started right up so I drove it down and got a new battery. Their tester said it was at 12.6 volts and 69% capacity. They didn't want to warranty it but after a few minutes of back and forth, Battery's Plus made good on it, so they deserve a thumbs up.

    Obviously there is an intermittent problem somewhere that is killing some of our batteries. Some on here have mentioned their car has to be started every couple of days or their battery dies. While others say they can go months with no problems.

    Are there any real techs on here that have come across this problem ?
     
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  2. Mendel Leisk

    Mendel Leisk Senior Member

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    Look for phantom loads?

     
  3. sam spade 2

    sam spade 2 Senior Member

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    Maybe......maybe not.
    Some batteries just go bad; some the DAY after being installed.

    Some testing needs to be done but you will need a multi-meter for all of it.

    There are several pretty detailed threads on here already about chasing down "phantom drains" when the car is OFF.
    Sometimes it is not a phantom drain at all and ends up being something like a door not closing all the way and leaving the dome light on.
     
  4. VFerdman

    VFerdman Senior Member

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    You need a multimeter, a fuse puller, some information (watch the video Mendel linked) and some common sense. This is not something anyone on internet can solve for you. We can only offer "methods" of troubleshooting. If you've been wrenching on cars for ever, then you most likely have dealt with parasitic current draw before, but maybe not. In any case, best of luck and keep us informed. There are always useful lessons to be learned.
     
  5. Usle

    Usle Active Member

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    The first lesson prius drivers learn is never use acc to listen to the radio like any other car on the road, the 12v will drain in minutes, then will require a full charge to get back to normal.
    The prius comes with a deep cell battery that can be drained and recharged several times, if you have a non deep cell battery (aftermarket) that's a problem.
    If you have a parasitic drain like rodents chewing, you need to address that problem.
     
  6. bisco

    bisco cookie crumbler

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    since it happens so infrequently, might you have left a light on or door ajar?
     
  7. Grit

    Grit Senior Member

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    Well, when it comes to troubleshooting a battery then, guess I’m SOL.
     
  8. 1prius

    1prius Junior Member

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    Sorry for the delay guy's, been busy with life's BS.

    Thanks for the reply's but - what I was looking for was a tech that has found a common cause for this problem. That I need a VOM to find the problem is not a viable reply to an intermittent problem. The fact that it is "intermittent" greatly reduces the chances of finding anything useful.

    If you read through search results for "dead battery", you will see most folks are babes lost in a city park. A few of us have on going issues with 12v battery problems - like me !

    New batteries, like everything else can go bad in short order. That's why they have warranties. But to go from a full charge to 4.9v in less than 10 hours is not likely a defect. To save time here, go back and reread my complete OP. Obviously there was a drain that stopped as soon as I disconnected the battery to charge it. NO - there were no lights on etc and I have not had any trouble since. Like I said before it's intermittent. Just don't want to be caught on the road with another dead 12v from the same problem.

    Are there any Toyota techs on here or am I barking up the wrong tree ?

    Thanks
     
  9. Grit

    Grit Senior Member

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    Like all dressed up & ready to be hit on? I'm going to need to see photos of these... city parks.
     
    #9 Grit, May 21, 2019
    Last edited: May 21, 2019
  10. 1prius

    1prius Junior Member

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    Grit - don't you know they call the cops on us old farts hanging out at the park these days ? We're suppose to go blind or at least not appreciate the mighty fine work nature has done !
     
  11. VFerdman

    VFerdman Senior Member

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    Barking
    Definitely barking up the wrong tree. Even if there was a Toyota tech here they would not be able to diagnose your problem over internet. You need hands on work. Strangers on internet can’t help in this case.
     
  12. Mendel Leisk

    Mendel Leisk Senior Member

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    Gonna stop watching this thread.
     
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  13. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Just a shade-tree wrencher, but here goes.

    The most common causes for a dead battery in no particular order:

    dome light left on

    door left ajar (triggers dome or trunkspace light)

    aftermarket OBD dongle that isn't smart enough to shut itself off when the car shuts down:
    The onboard diagnostics port supplies constant power to any interface plugged into it. It is the responsibility of the user to make certain the interface "dongle" is either disconnected or shut off to prevent drain. Some people use these devices to connect smartphone apps like Torque or Dr. Prius to monitor their cars. Some people have dongles from the insurance company to monitor their driving habits for rate reductions. Some people have jealous spouses who install GPS trackers.​

    smart key system:
    This is a complicated one. The car normally uses very little electricity from the battery to listen for radio signals from the smart key. But if it thinks the key is near, it wakes up a bit more, using more power. Some owners have found that a key stored near or in the car is a recipe for a dead 12v battery. This is not limited to the Prius, several other brands are using similar smart keys now and they're getting the same disappointments the next morning.

    I don't have a car with a smart key system, so I haven't had the opportunity to play with this firsthand. However, I have read about it in a number of threads on this board and other forums related to other cars with similar RF key systems.

    The prius has a mechanism to let you temporarily disable the smart key system to eliminate the normal parasitic draw for long term parking and storage. Owners' manual has details on usage.

    Good luck!​
     
    #13 Leadfoot J. McCoalroller, May 21, 2019
    Last edited: May 21, 2019
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  14. 1prius

    1prius Junior Member

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    Ferdman, I don't mean to be rude but -
    The whole point of my posting was to see if there was a real tech, that found a common cause for an intermittent beyond the typical fun. IE; a computer glitch or something. And yes most people on the net are just trying to be helpful but are not techs of any kind. That said, I am on a few groups that actually have techs, that also are fans of the pertinent ride and are knowledgeable about some obscure issues that have come up. Never know if you don't ask.

    Leadfoot, thanks for your reply about the key fob fun. Perhaps it could be a relay in the monitoring system sticking.

    Is there some way to delete the fob system and just have a keyed ignition ?
     
  15. sam spade 2

    sam spade 2 Senior Member

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    You are making a lot of BAD assumptions here.

    Without a VOM, neither you nor a "technician" is likely to ever find the problem in a timely manner.

    An internal battery defect can make a battery go from 12.6 to (pick any number less than that) in any amount of time.

    Typically, people who work in the service department are not well trained "technicians" and some don't even really understand electricity.

    What we have here is another case of "Dont' confuse me with facts, just answer my question exactly as I asked it, because my mind is already made up."

    Alas, it is likely that nobody can help you.......because you aren't listening.
    P.S. I've been an Electronics Engineering Technician for about 50 years now.
     
  16. RRxing

    RRxing Senior Member

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    Obviously...
     
  17. 1prius

    1prius Junior Member

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    SS2 - Like I said READ MY OP !
    The battery would not take a charge with the cables hooked up. Once the negative cable was disconnected, it took a charge ! How ever it would only take 60% as it had been fried by the extreme draw down. Nothing was turned on and the doors were closed tight. It was not the battery as it took a partial charge and still started the car the next morning. I would not hire you to read me the comics as you obviously don't have very good reading/comprehension abilities !

    I asked a specific question and got generic answers. A VOM will only tell you what is happening at that moment on what ever line it is applied to. It won't tell me if the computer is malfunctioning, and even less about an intermittent issue that is not happening at the moment. I don't expect to find the answer in short order since it only happens about once a year. Just hoping to get a head of it. Some EE you are!!!

    BTW; Met electrical engineers that shut down the production line 3 times, because they could not figure out they needed to use a variable resistor for fine tuning - LOL !!

    Others have had the same issue I am having and got many of the same reply's. This is a real problem for some of us and deserves attention on the forum. I would think it should have a sticky to try and find the answer as this has been reported for several years.. And not chastised for not being a simple fix.

    One thing you got right was that many techs these days are little more than print-out readers and parts changers. A lot of the work I do is correcting others mistakes. But it is nice to get knowledgeable advice from others when available. So I asked a question and came up empty.

    If you don't have any constructive criticism or experience with the problem at hand please go away - Thank you !
     
  18. sam spade 2

    sam spade 2 Senior Member

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    If YOU can't recognize good advice when you see it..............

    YOU don't know what you don't know. Sad.
     
  19. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    OP:
    First thing first:
    I'll do you the favor of answering your question...

    No.
    I'm not aware of any Toyota techs that regularly post here.
    At least I don't remember anyone who regularly posts here that admits to it.

    No.
    There is no "common" cause for G3 battery failure other than what we in the electronics field call a dead short between the seat and the steering wheel.

    The Aux battery is a known issue with the G3, (too small, improper voltage management system, etc...) AND you have to remember that your car is nine years old now, has SOY BASED WIRE (it tastes like Doritos to mieces) and WE don't know what interesting alterations that have been made to the wiring, any accidents that have occurred with the vehicle or much of anything else, other than you're frustrated .

    So:
    Since you're not listening to any advice offered thus far, and since I've answered your questions...
    I wish you fair winds and following seas!
    ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

    Advice for people searching for the reason why their aux (12v) batteries keep failing:

    1.) Bad batteries are sometimes....bad batteries. Prius Aux batteries need to be NEW BRAND NAME batteries....not some cheap recycled unit like they sell at places like Battery Plus. Unlike the cars you grew up with, the 12v battery in a Prius doesn't "start the car."
    It boots the car up. This is a VOLTAGE thing, not a current thing. If you do not know why this is important, then do not be discouraged!!
    As we see above, sometimes KNOWING that you do NOT know something is a good thing.

    2.) In a car with a proper voltage management system, you can leave the dome light on, walk away, come back an hour later and the dome light will be OFF. It does NOT work this way with a G3 Prius!
    The headlamps will auto-shut off. (my headlamp switch stays on all the time) but if you leave your dome light on you will suck your aux battery dry.

    3.) You need a real meter to really measure individual circuits to determine whether there is a parasitic current draw, or the batteries are dying from cockpit error.
    Yes.
    Sometimes the current leak can be intermittent, but a properly trained electronics technician will always verify FIRST what they can verify FAST.

    THIS is one of the better videos I've seen to make sure that you do not have a consistent parasitic current draw.
    NOTE: The G3 Prius has an ironically named "Smart Key"
    Make sure that this is away from your car before you test the individual circuits since the proximity detector will 'wake the car up.'



    Anyone interested in troubleshooting beyond this instead of just grousing, please mention any aftermarket equipment that's been wired to the car, wrecks, past rodent infestations, flash flooding, etc in your initial post.

    Good Luck!!
     
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  20. Ed Beaty

    Ed Beaty Active Member

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    Superb rundown on the answer, and GREAT video linked there. Thanks.