12V battery appears dead, won't jump, then magically works

Discussion in 'Prime Care, Maintenance and Troubleshooting' started by PHEVisthefuture, Jul 7, 2026 at 8:52 PM.

  1. PHEVisthefuture

    PHEVisthefuture Junior Member

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    Good evening,

    Thanks for all your help on this wonderful forum. I have an interesting issue with my 2017 Prius Prime (~109k miles), purchased used last year.

    Two days ago, I went to wash the vehicle and sprayed the body, wheel wells, and rear trunk profusely to get grime and bugs off the exterior. I don't know if this is related, but shortly after, the following happened:

    While trying to set the "delayed charging" time via the steering wheel GUI, I received a "12V battery low, set parking brake" message on the dash. Then, I received a "service traction control" and "service ABS", along with power steering warnings and a dozen other warnings I could not record because they scrolled through so fast. The car lost its center screen, dash was dim, and had all sorts of warnings going off.

    Within 5 minutes, I connected a Noco GB70 jump pack and tried to charge the 12V battery. The jump pack errored out, giving the "unable to charge" message, even though the polarity was correct and the jump pack was fully charged (and known working). So I let the car sit, and drove my other vehicle to work for 2 days.

    Yesterday, I purchased a genuine Toyota True Start 00544-H4470-TS battery from a local Toyota dealer. It was around $250 and appears to be the stock AGM battery.

    Today, after work, I was intending to replace the battery since the car has been dead for 2 days. The last time I tried to start it with the jump pack all I got was relay clicks under the hood and barely any electronics. Now, out of the blue, the car started up, drove around the block, and everything is back to working again.

    And here's the kicker - the jump pack had not been connected for over 24 hours, the car was dead as a door nail except for the warnings last time.

    Should I replace the 12V battery with the one I just purchased or is this a sign of other issues? I have never owned a vehicle in 20+ years that had a "dead" battery which came back to life like this.

    Thanks in advance for the help!
     
    #1 PHEVisthefuture, Jul 7, 2026 at 8:52 PM
  2. VelvetFoot

    VelvetFoot Senior Member

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    I am curious how old the battery is.
     
    #2 VelvetFoot, Jul 7, 2026 at 9:11 PM
  3. BiomedO1

    BiomedO1 Senior Member

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    1. I don't understand how you would charge a battery with a jump pack.
    2. If you don't have a good connection to the battery; jump pack clamps, your jump pack won't engage. There is a procedure to over-ride the jump-pack ECU and force power to the clamps.
    3. How old is the battery and has it been tested? Your car will start all the way down to about 10.5VDC. Letting the battery rest; probably allowed it it regenerate up beyond 10.5VDC - but if you put a meter on it I'd bet it's low.
    4. When you claimed that your battery was deader than a door nail; did you verify that with a volt meter?

    YMMV
     
    #3 BiomedO1, Jul 7, 2026 at 9:19 PM
  4. BiomedO1

    BiomedO1 Senior Member

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    1. I don't understand how you would charge a battery with a jump pack.
    2. If you don't have a good connection to the battery; jump pack clamps, your jump pack won't engage. There is a procedure to over-ride the jump-pack ECU and force power to the clamps.
    3. How old is the battery and has it been tested? Your car will start all the way down to about 10.5VDC. Letting the battery rest; probably allowed it it regenerate up beyond 10.5VDC - but if you put a meter on it I'd bet it's low.
    4. When you claimed that your battery was deader than a door nail; did you verify that with a volt meter?

    YMMV
     
    #4 BiomedO1, Jul 7, 2026 at 9:21 PM
  5. PHEVisthefuture

    PHEVisthefuture Junior Member

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    Here is the battery, if the number on the top is the date code, then it’s December 03, 2017.
     

    Attached Files:

    #5 PHEVisthefuture, Jul 7, 2026 at 10:26 PM
  6. PHEVisthefuture

    PHEVisthefuture Junior Member

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    Yes, I did press the override which allows the jump pack to “trickle charge” the battery. I don’t know if all jump packs can do this, but I’ve literally did the “force trickle charge / override button” and hooked an inverter to the clamps, and could power a small DJ speaker (it didn’t last for long, the current wasn’t there) but it DOES have the ability to “trickle charge”, just at limited amps…

    Voltmeter says 11.8V when sitting but I don’t think the battery has the CCA of a new one, it appears to be 8-9 years old.
     
    #6 PHEVisthefuture, Jul 7, 2026 at 10:30 PM
  7. BiomedO1

    BiomedO1 Senior Member

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    It doesn't require much CCA; since it only closes the main relays. Get the battery load tested, free, at any auto parts store to verify.

    There's no 12V trickle charge function that I can find; just a jump start function. Some of these can recharge phones or anything with a USB charging port. FWIW; when the unit flashes red - the lithium battery is too hot, dumping it's load too fast.
    https://no.co/media/wysiwyg/downloads/User_Guides/Boost/GB70-User_Guide_03.07.2025A.pdf
     
    #7 BiomedO1, Jul 7, 2026 at 10:45 PM
  8. VelvetFoot

    VelvetFoot Senior Member

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    Who messes around with a 9 year old battery? I'd replace it first thing.
     
    #8 VelvetFoot, Jul 8, 2026 at 7:41 AM
  9. Mendel Leisk

    Mendel Leisk MMX GEN III

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    Reading Noco's literature, I get the sense it's purely a jump starter for automotive batteries, and it's charging ability is limited to small batteries, like cell phones, lap tops. For charging an automotive 12 volt battery, a smart charger (keep amp rating to 5 or less), plugged into 120 volt AC, is what you need.

    Also would be good to assess the battery, with an electronic load tester, see where it's at.
     
    #9 Mendel Leisk, Jul 8, 2026 at 10:57 AM
    Last edited: Jul 8, 2026 at 11:24 AM
  10. ColoradoBoo

    ColoradoBoo Senior Member

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    Yep 12-volts seem to last a LONG time in our two Prius but I went ahead and replaced mine in the 2017 a couple of years ago when it was testing at 70%. A good battery tester can tell you the condition but, at this point, best to just replace it.

    FWIW, I bought a Toyota TrueStart 12-volt battery to replace it from my dealer and that thing is, still, testing 100% after two-years....impressive!!
     
    #10 ColoradoBoo, Jul 8, 2026 at 11:20 AM
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