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Charging a dead 12 volt battery

Discussion in 'Gen III Prius Care, Maintenance & Troubleshooting' started by jstraw20, Sep 13, 2012.

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  1. jstraw20

    jstraw20 Member

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    My dad's Gen III has been sitting garaged for almost a year now, and of course the 12 volt battery is dead. Firstly, it's sitting in a one car garage, and secondly I have a Gen II so a straight jump isn't possible. I have a trickle charger that should be able to bring the 12 volt back up in 15-19 hours, but here's my question:

    Maybe I'm being lazy, but I'd rather not deal with climbing in the back to release the hatch and running an extension cord so I can get the charger close enough to hook straight up to the battery... Will hooking the charger up to the jump ports under the hood work?
    DAFTEK likes this.
  2. Buzzhead

    Buzzhead Airhead Armada Lurker

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  3. eric1234

    eric1234 Member

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    Although you certainly cant jump any other car with your GEN II, since the actual current needed to "start" your GEN III is fairly minimal, I'd venture a guess that you could probably jump your GEN III prius with your GEN II prius... You could use jumper cables to connect the battery from the GEN II to the under hood terminal of the GEN III - just be sure NOT to screw up the polarity...


  4. After almost a year, it may not charge up right.
  5. xpcman

    xpcman Active Member

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    I hope the HV battery is not also dead. Your Toyota dealer will need to get a special charger shipped in before they can charge it.
  6. jstraw20

    jstraw20 Member

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    Well, I'll hook it up this weekend and we'll see what happens. <crossing fingers>
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  7. DAFTEK

    DAFTEK Junior Member

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    Please post the results, i also plan to store my gen3 for a year or more and i usually just disconnect the terminals after a full trickle charge. My concern is the HV battery.


  8. You would be better off finding someone dependable to start the car once a month, or lending it to someone you trust, or selling it. Neither battery can sustain a shelf life of more than one year. I may be wrong, so check it out good.
  9. jstraw20

    jstraw20 Member

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    I should point out that my initial post was a bit off. The car has been garaged for a year, but the 12 volt only died last April, while I was away on vacation. Prior to that I'd been putting the car in ready and leaving it that way for 2-3 hours at a time a couple of times a month. The HV battery was in a good SOC at the time the 12 volt went dead, so hopefully it still has a decent amount left.

    One way or another the car is getting out of that garage once I get it running again. If push comes to shove and I have to sell it, whoever buys it is going be getting an excellent deal. The car only has a hair over 5000 miles on it and apart from the dead 12 volt it's in mint condition.


  10. My last post was actually pointed to daftek
  11. jstraw20

    jstraw20 Member

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    DOH! I guess I'm so concerned about this car firing up that I'm trying to convince myself that it will without a hitch.


  12. Wish you luck, why don't you keep the 2010 and sell your 2007? providing you get the 10 going.
  13. jstraw20

    jstraw20 Member

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    Update: Trickle charging via the jump terminals under the hood didn't work. The charger charged for about 20 minutes, then declared the battery charged and dropped into maintenance mode. In reality all it did was get the battery from just about flatline up to the point where the interior lights were dimly glowing, but not enough to allow the car to go into ready. Part of the problem was the brake pump was trying to pressurize the system every couple of minutes and I'm guessing the fluctuations in load tricked the charger.

    I didn't have time to experiment today, but next time I'm going to try hooking up directly to the battery. I'll also look thru the threads and see if I can figure out how to disable the SKS on a Gen III as I think it was detecting the fob while I was charging it. If that doesn't work I'll just pull the battery out and try charging it while it isn't connected to the car...
  14. John H

    John H Senior Member

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    Personally, I would get a new 12V battery and install it. The stock OEM 12v battery doesn't like being completely discharged, at least that is the case with the gen2. I would replace with a deep cycle design, like the optima yellow top, if you plan to store the vehicle again. I hope your HV battery isn't toasted, I don't think they like to sit in storage either. I would drive it around one weekend a month minimum, burn a gallon of gas and replace it.
  15. jstraw20

    jstraw20 Member

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    Logic completely dictates that I do that since we're talking about a near mint car with super low miles vs mine which is pushing 75k. But I own my car free and clear, while the Gen III is leased. I need to settle things with Toyota Finanial asap and 1) I'd rather not assume the lease as I don't like the terms and 2) I don't think I could get enough for my Gen II to pay off the lease. Also, I love my car and while I like my dad's Gen III it would only remind me of his recent departure. So for now... I'm keeping my car :)
  16. jstraw20

    jstraw20 Member

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    If I can't get the current battery to hold a charge then that will absolutely be my next move.
  17. Financially, your decision makes absolute sense. Very sorry to hear of your Fathers demise.
  18. szgabor

    szgabor Active Member

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    I have successfully booted up my GEN II & GEN III with a badly discharged but not damaged battery with the trickle charger connected (under hood port) the car simply went into Ready and all was fine after that. I do not know if I did something risky or not. so of course it is your car so you figure it out.
  19. Buzzhead

    Buzzhead Airhead Armada Lurker

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    Sorry the jump terminals didn't work. To disable the SKS, pull the ECS-B2 fuse under the hood. You won't lose any settings.
  20. jstraw20

    jstraw20 Member

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    I don't think any damage was done since the car did sort of come to life once the trickle charger was hooked up. My best guess is that the capacitor bank that feeds the brake pump was completely discharged and was soaking up the current from the trickle charger, but then discharging before the capacitors were completely charged. I'm going to pull the battery out and try charging it directly tomorrow. If that doesn't work then I'll admit defeat and drop the $$ on a new battery.