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12V battery won't hold charge

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Johnny KIlo, May 2, 2015.

  1. Johnny KIlo

    Johnny KIlo Junior Member

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    About 4 months I accidentally reversed the polarity when jumping my car (I know, please save me the lecture) and fried my 12V battery and blew the fusible link. I replaced it with an Optima yellow top but due to other issues I haven't driven the car since about that time. Last week I got most of the other issues resolved and tried starting the car, nothing. It was reading less than a volt on the voltmeter. I used my portable jump starter and got the car started. I only drove it to the gas station (1 mile round trip) to fill my tires and back. I went to start it the next day and nothing again. I thought maybe I didnt charge the battery enough since I hadn't been driving it. I charged it overnight using a wall charger and again the next day it wouldn't start. Yesterday I jumped it again and drove it about 20 minutes, about half at low speeds (<30 MPH) and half at higher speeds. I got home put the car in park, but still on, and checked the voltage again, about 13.8 V. Turned the car off and checked again and I could see the voltage dropping like a rock. Within about 30 seconds it was down to 6V and within another 30 seconds it was so low that I didnt have any interior lights or dash lights.

    It seems to me like the battery is bad. However after I "fried" the original battery I had similar issues. In fact the reason I had to jump it in the first place is because the battery died a few times in the same day. Could something be killing the battery?

    thanks.
     
    #1 Johnny KIlo, May 2, 2015
  2. bisco

    bisco cookie crumbler

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    possible. but it's also possible that the new battery just sat around too long and croaked. there is a spec on how much the battery should be draining when the car is off. you may want to find it, and measure yours to see if there is some parasitic drain going on, it has happened before.

    you can also recharge your battery on the bench, and then see how it holds up, before reconnecting to the car.
     
    #2 bisco, May 2, 2015
  3. exstudent

    exstudent Senior Member

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    Look-up the specifications of your 12V battery charger. AGM compatible/setting? Output setting when you charged overnight: .5amp, 1amp, 4amp? Too low of an output, and the battery won't charge. Too high of an output, and you'll kill the battery.

    How are you reading the voltage? W/ a DVM (Digital Volt Meter)? Is this DVM reliable/accurate?

    It does sound like the battery is bad. However, if the 12V battery charger you used was a trickle charger (say .5Amp or 1Amp), it will never recharge a battery that has been severely discharged, as yours sounds to be. It may be time for a new 12V battery charger.

    Read Optima's "Recommended Charging Information."DS46B24R YELLOWTOP® Prius® Auxiliary Battery 8171-767 | OPTIMABATTERIES
    Battery Charger: 13.8 to 15.0 volts; 10 amps maximum; 6-12 hours approximate
    ​

    EDIT: If your Prius has SKS, you really need to get a 12V battery from Toyota or the Bosch/Exide. All three of these are 45Amp-hr batteries; these were supplied w/ the car originally. The yellow top Optima is 38Amp-hr, and would be fine for a non-SKS Prius, b/c there isn't the continuous drain of the SKS system look/waiting for the fob to come w/in range. Obviously one could turn off the SKS system too, which is a good idea when an SKS car will sit for a long time (say 7days or longer of disuse).
     
    #3 exstudent, May 2, 2015
    Last edited: May 2, 2015
  4. Johnny KIlo

    Johnny KIlo Junior Member

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    I am using a DVM to measure. The charger is only 1.2 AMPS with a 6/12 volt switch.

    I never actually took my other battery in for the core so I decided, what the hell I'll measure it, 5.4 volts. I think terminals need to be cleaned, when I touch the probes to the top of the terminals I get 0V, but when I touch near the base of the terminal post I am getting the 5.4. The original battery is about a year old and its an AGM 46AH. I am going to see if it takes a charge.

    Also I do have the SKS so that is probably giving me headaches.

    EDIT: Ignore the part about the terminal posts, I didn't have the metal part of the probe touching the post all the way. I am getting consistent voltage now.
     
    #4 Johnny KIlo, May 2, 2015
    Last edited: May 2, 2015
  5. bisco

    bisco cookie crumbler

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    the sks isn't normally a problem. i leave my prius every winter for 5 weeks, and still have 12.7 volts when i get home.
     
    #5 bisco, May 2, 2015
  6. Patrick Wong

    Patrick Wong DIY Enthusiast

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    If you have not driven the car for four months, that idle period is the reason why the 12V battery died. A wall-wart charger will be ineffective. As previously suggested, you need to use a real battery charger, intended for AGM batteries, and a charging rate of 10A (for Optima) or 4A (for the original equipment GS Yuasa battery). And, leave that charger to run at least overnight, or until the charger says the battery is fully-charged.

    Even if you use an adequate charger, the battery may be beyond recovery. You probably can file a claim under the Optima battery warranty. In the future, if you need to leave the car for more than a month, you should fully-charge the 12V battery, then disconnect it for storage.
     
    #6 Patrick Wong, May 2, 2015
    Mendel Leisk likes this.
  7. Mendel Leisk

    Mendel Leisk Senior Member

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    Patrick, would just disconnecting the negative cable be effective disconnection?
     
    #7 Mendel Leisk, May 2, 2015
  8. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Yes
     
    #8 Patrick Wong, May 2, 2015
  9. Johnny KIlo

    Johnny KIlo Junior Member

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    I bought a 2/6/10 amp AGM specific charger (Schumacher SSC-1000A from Advanced Auto Parts) and charged the "old" battery (World SourceOne Exact Fit 46aH) and it seems to be holding a charge well. I was able to start the care a few times today with no issue.

    I checked the voltage from the diagnostic mode and I was getting about 12.6 V so i think i am good shape.

    Thanks guys
     
    #9 Johnny KIlo, May 3, 2015
  10. bisco

    bisco cookie crumbler

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    well done!(y)
     
    #10 bisco, May 3, 2015
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