1. Attachments are working again! Check out this thread for more details and to report any other bugs.

No voltage measured across "12V" battery after recharging

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by gdowdy3, Sep 1, 2024.

  1. gdowdy3

    gdowdy3 New Member

    Joined:
    Oct 8, 2023
    20
    3
    0
    Location:
    California
    Vehicle:
    2007 Prius
    Model:
    N/A
    Hello folks,

    Last weekend, I tried to use my Prius after it sat idle for a month and a half. However, I found that the car was utterly unresponsive: the door locks wouldn't work, the ignition button did nothing, no dash lights, and so on. I thought that the "12V" battery might be dead as a result of the prolonged period of inactivity. I tried to measure the voltage across this battery with my voltmeter. It reported no voltage.

    So, I tried to charge my battery with a "DieHard 71219 6/12V Shelf Smart Battery Charger". The charger showed that it was charging for about 2 hours, then declared the battery to be fully charged. However, still the car is unresponsive. Furthermore, when I try to measure the voltage across the terminals of the battery, I am again seeing 0 V.

    The battery is pretty new. I bought just late last year. Furthermore, I bought it from a local Toyota dealer, so it's not like it's some sketchy off-brand.

    Anyone have any analysis of the situation? Do I just have a bad battery? Are there any other tests you recommend before coming to this conclusion?

    Feel free to ask follow-up questions. I'm happy to provide additional details that might help you diagnose the problem.

    Garrett
     
  2. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    24,728
    16,091
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    Sounds like the month and a half without charge has done in the battery.

    If it was from a Toyota dealer late last year, you may be eligible for at least a pro rata and possibly full price toward a replacement if you take it back to them. Before covering it, they will put it on their own tester to see if it's really kaput.
     
    Brian1954 likes this.
  3. mr_guy_mann

    mr_guy_mann Senior Member

    Joined:
    Sep 3, 2020
    3,612
    1,666
    0
    Location:
    NJ-USA
    Vehicle:
    2006 Prius
    Model:
    Four
    I would check that your meter actually reads (DC) voltage correctly.
    Many "smart chargers" won't work correctly if the target battery is completely dead.

    Posted via the PriusChat mobile app.
     
  4. rjparker

    rjparker Tu Humilde Sirviente

    Joined:
    Jun 6, 2008
    8,294
    4,915
    7
    Location:
    Texas Hill Country
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
    Agree. Also make sure your voltmeter is not on AC. It will read zero dc in that mode no matter what. Simply check a 1.5 or 9v battery that you have in a drawer or a remote.
     
  5. gdowdy3

    gdowdy3 New Member

    Joined:
    Oct 8, 2023
    20
    3
    0
    Location:
    California
    Vehicle:
    2007 Prius
    Model:
    N/A
    Thanks for weighing in, guys!

    Fortunately, my wife has a Prius with a working "12V" battery, which allows me to take comparative measurements. If I try to measure the voltage of her "12V" battery with the same voltmeter, it reads 12.4 V, and also reports "DC". So I don't think my voltmeter is the problem.
     
  6. gdowdy3

    gdowdy3 New Member

    Joined:
    Oct 8, 2023
    20
    3
    0
    Location:
    California
    Vehicle:
    2007 Prius
    Model:
    N/A
    Any other suggestions for what I should check before I take the battery back to the Toyota dealer?
     
  7. rjparker

    rjparker Tu Humilde Sirviente

    Joined:
    Jun 6, 2008
    8,294
    4,915
    7
    Location:
    Texas Hill Country
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
    If it’s a true zero volts it has an open connection internally.

    I would swap batteries to know for sure. But you should get a new battery from the dealer.
     
  8. MAX2

    MAX2 Member

    Joined:
    Aug 12, 2024
    371
    87
    10
    Location:
    Third Rock from the Sun
    Vehicle:
    2007 Prius
    Model:
    N/A
    When you charge with a charger, what is the voltage at the battery terminals during charging?
     
  9. gdowdy3

    gdowdy3 New Member

    Joined:
    Oct 8, 2023
    20
    3
    0
    Location:
    California
    Vehicle:
    2007 Prius
    Model:
    N/A
    That's a good question. I wondered the same thing. However, when I try to measure the voltage across the battery terminals during or right after charging, I'm not seeing any voltage. Only after making this observation did I notice that my voltmeter says "DISPLAY ON > 10 V", which I take to mean that it won't report anything less than 10 V. If that's true, then all I can say with confidence is that the voltage is less than 10 V.
     
  10. BiomedO1

    BiomedO1 Senior Member

    Joined:
    Mar 27, 2021
    1,696
    870
    0
    Location:
    SacTown, Ca
    Vehicle:
    2021 Prius Prime
    Model:
    LE
    I don't like 'smart chargers' because they don't charge a fully dead battery or tell you there's an open in the battery. You can disconnect the battery from the car to see if you have a few volts - then try to recharge again. There should also be some sort of manual over-ride function on that 'smart charger' to force a charge.
    Alternatively, you can jump start the car. Use a jump pack (same deal with the jump pack as the 'smart charger') or move your wife's known good battery to that car to test. You may have a parasitic draw in that car because a month of no-start shouldn't take a newish battery down to zero, unless the battery itself is defunct.

    Good Luck....
     
  11. gdowdy3

    gdowdy3 New Member

    Joined:
    Oct 8, 2023
    20
    3
    0
    Location:
    California
    Vehicle:
    2007 Prius
    Model:
    N/A
    I'm realizing that this means that some of my prior messages were unfortunately misleading. Anywhere where I've said I measured "0 V" or "no voltage", this should be reinterpreted as "no more than 10 V".
     
  12. BiomedO1

    BiomedO1 Senior Member

    Joined:
    Mar 27, 2021
    1,696
    870
    0
    Location:
    SacTown, Ca
    Vehicle:
    2021 Prius Prime
    Model:
    LE
    Check for lose battery terminals - Clean and reattach them if your not sure. Low current draw a battery looks fine - but under high current draws the connectors will spark and disconnect. A rookie mistake I've seen several ASE certified mechanics make!!

    Where are you placing the test leads, on the battery post or terminals? Press the test terminals in and rotate to make sure you've got a good connection. Make sure your not trying to take a reading off an accessory powered line.
     
  13. gdowdy3

    gdowdy3 New Member

    Joined:
    Oct 8, 2023
    20
    3
    0
    Location:
    California
    Vehicle:
    2007 Prius
    Model:
    N/A
    Another update that might be important... Yesterday, even though I had already tried to charge the battery once, and the charger told me that it was "charged" after 2 hours, I decided to try to charge it once again. So I hooked up the charger again, and the thing sat in the "charging" state for something like 8 hours(!) before it finally said "charged".

    Furthermore, when I then tried to start the car, I could see *some* signs of life which were all previously absent. In particular,
    1. There was a little dash light indicating that a door was open.
    2. The two little green lights on either side of the key fob slot were glowing.
    3. There was an orange light on the ignition button.
    4. When I pressed the brake pedal, I could hear a clicking sound.
    5. I could turn on the dome light, but it was very faint.
    However, I still could not start the car. Pressing the ignition button had no apparent effect.

    This morning, I confirmed that I could still turn on the dome light. It was still very dim. This suggests to me that the battery successfully held at least some charge overnight.

    I once again hooked up the charger. Despite the fact that it had declared the battery to be fully charged last night (for the second time), this morning, it again said that it was "charging".

    I'll add that the battery charger manual says that it could take up to 10 hours to charge a "50% discharged battery".

    So, everything taken together, the hypothesis that's developing in my mind is that the battery charger is, indeed, charging the battery, but that it just keeps prematurely declaring the job to be done. I'm planning to leave it charging today as long as I can to see if I can get more signs of life from the car as a result.

    Any alternative interpretations of the facts?
     
  14. gdowdy3

    gdowdy3 New Member

    Joined:
    Oct 8, 2023
    20
    3
    0
    Location:
    California
    Vehicle:
    2007 Prius
    Model:
    N/A
    I'm pressing the leads of my voltmeter directly on the battery posts. I used the same method to successfully measure the voltage on my wife's Prius battery.
     
  15. gdowdy3

    gdowdy3 New Member

    Joined:
    Oct 8, 2023
    20
    3
    0
    Location:
    California
    Vehicle:
    2007 Prius
    Model:
    N/A
    I will also add that my car insurance is through Metromile (now Lemonade), which means that I have one of those sensors stuck in my OBD2 port that reports my driving distance to Metromile. I'm pretty sure that this thing continues to draw power from the 12 V battery even when the vehicle is off. If so, that would be the "parasitic draw" you've inferred.
     
    BiomedO1 likes this.
  16. rjparker

    rjparker Tu Humilde Sirviente

    Joined:
    Jun 6, 2008
    8,294
    4,915
    7
    Location:
    Texas Hill Country
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
    Parasitic draw is in every car. Normal is around 25 ma in a Prius. Measure it with a meter described below.

    It seems you are having a very difficult time with a very basic problem. Your meter seems suspect, I have never heard of one that said display on greater than 10v. A $5 Harbor Freight meter is better than that.

    Easy and free solution to the diagnostic- remove battery and take to an auto supply and have it load tested. If it fails take it to Toyota for a free replacement.
     
    BiomedO1 likes this.
  17. BiomedO1

    BiomedO1 Senior Member

    Joined:
    Mar 27, 2021
    1,696
    870
    0
    Location:
    SacTown, Ca
    Vehicle:
    2021 Prius Prime
    Model:
    LE
    Yep, unplug that and keep recharging. Jump start the car if you get impatient.

    Good Luck.

    PS you may get some DTC codes - more than likely related to the dead battery & low sensor voltages. Once you get the car running again - clear the code and see if any of them come back....
     
  18. BiomedO1

    BiomedO1 Senior Member

    Joined:
    Mar 27, 2021
    1,696
    870
    0
    Location:
    SacTown, Ca
    Vehicle:
    2021 Prius Prime
    Model:
    LE
    LoL, those Harbor Freight DVMs are the ones I use on my overseas mission work. Gotta love those free DVM coupons. So far, two has been crushed in transit and one I gave away to the local 'fix everything guy'. Poor guy was using his fingers to see if a line was "Hot". Showed him where the internal battery & fuse was.

    They're good enough in a pinch...
     
  19. rjparker

    rjparker Tu Humilde Sirviente

    Joined:
    Jun 6, 2008
    8,294
    4,915
    7
    Location:
    Texas Hill Country
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
    First it should be “any alternative interpretations of the observations.” Facts are yet to be determined.

    Assumptions often mislead us as well and cause a blind eye to be given to the real issue.

    A bad battery can have 5% of its capacity left. You don’t measure capacity with a voltmeter, a (under) load tester is needed.

    With very low capacity, a map light might draw a bad battery quickly below the 10.5v which my “observations” over 450,000 miles of hybrid ownership is needed to Ready the car.
     
  20. MAX2

    MAX2 Member

    Joined:
    Aug 12, 2024
    371
    87
    10
    Location:
    Third Rock from the Sun
    Vehicle:
    2007 Prius
    Model:
    N/A
    There are 6 cans on a lead battery, each of which produces a little more than 2 volts. In total, more than 12 volts.
    When one of the battery cans is shorted inside, the battery will not exceed 10 volts.
    Most likely, this is what is happening to you. It is possible that even two cans are shorted inside the battery, then 8 volts in the end, even after charging.