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solving empty 12 volt auxiliary battery problems

Discussion in 'Gen 2 Prius Technical Discussion' started by fsksol, Dec 13, 2009.

  1. fsksol

    fsksol Junior Member

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    2004 Prius
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    I am from Germany and have a question about the empty 12 volt auxiliary battery.
    Sorry about my bad english. My prius is from 2004.

    There is a problem with Prius II when the 12V battery is empty: the computer does not start. The car is not movable. There are a few suggestions to jumpstart from the engine compartment or directly at the battery in the boot. Both options have their issues.

    I am thinking for two different way's to solve the problem:

    1. I thought about starting the computer via the cigarette lighter in the middle console. The lighter must be wired on a permanent plus. Then you require a 12 Volt Dryfit Accu on which a permanent plus is to be put so the computer is turning on when connecting the voltage. In case the 12 Volt battery is empty the backup accu is losing its voltage right away. Therefore it is advisable to place a diode into the feed line of the control unit to prevent this loss. D1 in the Fig 1.
    The backup accu will be connected in a way that it is always charged but protected from dicharging by a further diode. This further diode will be bypassed by a calliper/ senser in case of an emergency start. Here is the question: where is the best place for the diode D1?
    2. The more elegance way, may bee, in Fig 3: a deep discharger protect the auxiliary battery, and a swich overbridged that (not draw). I have seen this by boat-yachting-assemly. Here is the problem: where is the point X of my drawing in the prius?

    Who has got experience on this or could give me a few tips on that?
     

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    #1 fsksol, Dec 13, 2009
  2. jayman

    jayman Senior Member

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    When I had my Prius, it couldn't keep the 12 vdc battery properly charged in severely cold winter city driving conditions: -40 C, headlamps on, electric defrost on

    I wired up a VDC Battery Minder to the battery, and that solved the problem. I also use the Battery Minder with my FJ Cruiser

    [​IMG]

    [​IMG]

    BatteryMINDer® Plus 12 Volt 1.33 Amp Charger-Maintainer-Conditioner (Desulfator) :: All :: Battery Chargers by BatteryMINDers.com

    I briefly went over your documents, the idea should work. If you have a problem causing unusual drain, that should be fixed first.

    Once a lead acid battery is discharged 2-3 times, it usually will have much reduced capacity and must be replaced
     
    #2 jayman, Dec 13, 2009
  3. richard schumacher

    richard schumacher shortbus driver

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    As Jayman wrote. If yours is the original battery you should first replace it.
     
    #3 richard schumacher, Dec 13, 2009
  4. fsksol

    fsksol Junior Member

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    It's the third battery, but it can happens with any battery, by leaving ON the inner lights or the parkinglights even if it is cold.
     
    #4 fsksol, Dec 13, 2009
  5. jayman

    jayman Senior Member

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    Unfortunately, most Toyota's do a poor job of preventing battery rundown. Even though my 2000 GMC Sierra truck was a POS in reliability, it would never let me leave on an interior light to drain the battery
     
    #5 jayman, Dec 14, 2009
  6. vertex

    vertex Active Member

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    A lot of people have replaced the battery with Yellow top batteries and gotten good results. I used a different, inexpensive approach, which some people objected to, with valid criticism, but I feel the issues they raise are not significant compared to the savings. I have left my lights on for hours, and found that the battery still will start the car easily.
    See:
    http://priuschat.com/forums/gen-ii-...66601-battery-replacement-economy-method.html
     
    #6 vertex, Dec 14, 2009
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