Battery Troubleshooting: Advanced Steps?

Discussion in 'Prius c Care, Maintenance and Troubleshooting' started by Bera33, Mar 15, 2021.

  1. Bera33

    Bera33 New Member

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    Hello,

    I understand this is *another* battery thread, however I'm posting since I've already tried all the troubleshooting steps offered in other threads I've seen and I'm at a loss for what's going on. The dealership I went to has been less than helpful with this entire situation. I'm hesitant to replace my current battery if I can't figure out what's causing my issue, in case it fries a third battery for me.

    I bought a used Prius C 2016 in September 2019. The only electrical work done on it has been the installation of an aftermarket car starter and some wiring was replaced by the dealership as squirrels decided to have a snack.

    January 2020, the OEM battery failed as I was unable to drive for two weeks - it discharged down to 2v and froze. I bought a replacement battery from a dealership and verified it was the right one. This battery was at 12.8v when I bought it from the dealership.

    The replacement battery failed on me at the beginning of February 2020. I was driving every 2-3 days and I had left the car for 3 days this time when it would not start. It measured at 6v, however it was not frozen so I was able to bring it inside and charge it up with a smart charger. Despite charging the battery fully and using the recovery mode afterwards to try and remove sulfation, the battery still seems to be in bad shape.

    The issue with the battery is that it will continually discharge itself, even when not connected to the car itself. It loses about .1v per day when not connected and between .15 and .2v when connected to the car. I contacted the dealership I bought the battery from and they offered a 'courtesy battery test'. Their test showed that the battery was "completely fine but deeply discharged". While I disagree with their assessment, Toyota Canada won't accept the battery under warranty as their battery test came back stating that the CCA's on the battery were good, which I don't think has anything to do with the issue at hand. The dealership now wants me to pay for any further testing, and if they do find something wrong I would still have to purchase a new battery from them.

    I'm having trouble doing a draw test as the battery is in the backseat - I need the door open to access the battery, which leads to an inaccurate test. I can tell you that with the door open the car draws 500mAh from the battery, but I don't know what the 'resting' rate is.

    My questions are:

    Are there any other tests I should be doing or can do to try and isolate if there's a draw issue vs. an issue with the battery itself? I don't want to risk buying a new battery just to have the same thing happen again.

    Should I just give up on Toyota Canada and try to find a new battery? I sure as heck don't want to purchase a new battery from them again.

    Is there anything else I might be overlooking or that I should be looking into?

    Thank you for your time!
     
  2. bisco

    bisco cookie crumbler

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    i can say that the battery shouldn't be losing a tenth a day, that's way too high. i go away for 9 weeks every winter, and the connected battery only loses a couple tenths when in good shape.

    even connected, it doesn't lose much unless the draw is too high. but short of figuring the draw spec, which someone may know, or renting the service manual, i would ask the dealer those questions.

    how much should a healthy battery self discharge per day, and what is the quiescent draw spec?

    try toyota corporate if they won't cooperate. if no luck from them, i guess a new battery is the only other solution.
    with squirrel wiring, anything could have happened. rodent damage usually means replacing the whole wiring harness, not repairs. about a $7,000. job iirc. often, insurance totals the car if it isn't worth it.

    all the best!
     
  3. kdfchannel

    kdfchannel Junior Member

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    disconnect the negative and use the test light to check between the ground cable and the battery - terminal.
     
  4. Bera33

    Bera33 New Member

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    Thanks for the ideas! The rodent wiring issue was from years before I bought the vehicle, it's a long shot that it might be the issue. The last person I bought the car from wasn't very car knowledgeable so I wouldn't be surprised if maybe it was something else entirely.

    I might rent the service manual if I'm going to do other work, otherwise I might just get a baseline and try to go to corporate.
     
  5. topshot

    topshot Member

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    Perhaps bad ground or aftermarket electrical add-on that's drawing significant power (radio, remote start, camera, etc) or faulty charging circuit. My understanding of the latter is the hybrid battery charges the 12V (there is no alternator like a normal car). I have never seen a schematic for that system, but if all the wiring checks out I would assume it must be some computer module that controls the charging.
     
  6. ChapmanF

    ChapmanF Senior Member

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    Nothing really "controls" the charging much. When the car is in READY, its 12 volt wiring is being supplied power from the car's DC/DC converter, downconverting from the high voltage system. The converter outputs a voltage around 14 to 14.7 volts, and since the 12 volt battery is part of the 12 volt system, it also sees that voltage, which is high enough to charge it. If the c is like the liftback, there may be a temperature sensor hanging in the air above the battery, and that temperature may be used to adjust the converter output voltage a little bit, but that's as close as the car ever gets to "controlling" the charging of the 12 volt.
     
  7. sam spade 2

    sam spade 2 Senior Member

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    It is highly likely that your "aftermarket remote starter" really is the cause of the problem.

    It is not unusual for a battery to "lose" a tenth of a volt over 24 hours for the first few days after being taken off a charger, or out of the car, but then it should stabilize after that. If it stabilizes at 12.5 or more, it should be fine.

    It is also possible that your new battery was not fully charged in the beginning. You can't trust the car to do that.
    Once it is discharged down to 6 volts, some damage likely was done. Not much maybe but some.

    AGM batteries generally do not create sulfation like a conventional wet cell does.
     
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