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Discharged start battery

Discussion in 'Generation 1 Prius Discussion' started by anon61, Jan 9, 2012.

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  1. anon61

    anon61 Junior Member

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    Your Vehicle Year:
    2001 Prius
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    I have just bought a 2001 Prius. Once, when I the car was not driven for a week, the battery was dead. I started with the help of cables and another car. Now, first step is to replace the battery.

    But, according to the toyota service records, the battery was replaced in 2008. And the present battery is an aftermarket battery, which the previous owner must have installed in 2010-2011. It's not a particularly cheap one. Plus owner minus two remembered that the car had a habit
    of discharging the start battery. Also, it has an aftermarket charger/engine heater/cabin heater
    system installed.

    I would like to rule out leak currents before I buy a new battery. Are there any known sources of leak currents in the first gen prius?
  2. R-P

    R-P Member

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    You say it's not a particularly cheap battery. Is it a deep cycle like a yellowtop? Then replacing it would be a shame, as they indeed are expensive AND can handle a full discharge a lot better than regular starterbatteries.

    Can't help you on the typical leak currents on a Gen I.
  3. anon61

    anon61 Junior Member

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    It's not very expensive either, 1175 SEK versus 1600 SEK for Toyota
    orginal. (USD 165 vs 225).
  4. usnavystgc

    usnavystgc Die Hard DIYer

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    My first suspect would be the aftermarket charger/engine heater/cabin heater system. I recommend you disconnect it, charge your battery and see what happens.

    I have never heard of any "leak currents" in the Gen I.
  5. anon61

    anon61 Junior Member

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    Yes that would be my first suspect too, excepting the possibility it was installed instead of finding the current leak.



    Wouldn't it be a simple matter for a car electric shop to measure if there is any current leaving battery? I realize that finding out where the current goes is (much) more work.



    That's good to hear. The BMW forums here in Sweden have more than a few posts on that. BTW, what's the common term? In Swedish, it is "läckström", leak current, or more informally, "tjuvström", thief-current.
  6. usnavystgc

    usnavystgc Die Hard DIYer

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  7. R-P

    R-P Member

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    I think leak current is correct (lekstroom in Dutch :D).

    Indeed simply adding a current meter after the battery will help. Then just start pulling out fuses to pinpoint where the fault may lie. I would probably even add my adjustable powersupply at this point because I am very anal about discharging batteries...

    Problem is obviously that especially the Prius doesn't have all fuses in one fuse-box, but you might already get somewhere with this.

    And obviously locate the (probably external, so not located in the fuse-box) heater-fuse if this is your prime suspect.

    One last remark: make sure you wait for a while. My motorcycle has a drain that has killed two $100 batteries so far. Using the above method, I found the leak-current was only 4mA (=clock), but soared to 150mA after a minute or so. 150mA will drain a small 14Ah battery in less than 100 hours, so leaving it over the weekend would already drain the battery more than half. And this effects total capacity pretty fast.
    My point: make sure you try to mimic the effects your car goes through: let it stand for a while so all systems come to a rest, have the automated heater start up, whatever you can think off.

    Good luck!
  8. anon61

    anon61 Junior Member

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    Good point. From the BMW forums it seems some cars draw a lot of current the moment the battery is connected. The computers apparently start up, and then after a while they go back to sleep.

    The heater system, Defa Warm-Up is a typical Swedish one driven by 220V AC from a wall outlet. It shouldn't draw much from the battery, not anything like an Eberspächer.

    Last night 6:30 the battery was at 12.8V, this morning at 7:00 it was 12.4V. A crude approximation, 75% capacity, 25% discharged, 0.25 * 40Ah = 10 Ah, 10Ah/12h =~ 0.8A, if the battery is OK.

    I don't have the equipment to measure this. The only multimeter I have is a small one for electronics. The company Biltema used to have DC only clamp meter that had resonable precision for low DC currents. The other reasonably priced ones (including low end Flukes) seems to have low precision for DCA.

    The current plan is to have a car electric shop do a proper battery test, and measure leak current. If it leaks, I will disconnect the Defa, and remove fuses and measure current over the open fuse sockets.

    I agree with usnavystgc that the Defa is the prime suspect, but it not the only one. According to the service history, the car seat heaters, the cd player, and the Defa system were all after-installed by the Toyota dealer. From the discussions about other cars, the rear window heater, and the diode bridge in the alternator.

    Is there a complete wiring diagram for the Gen 1? I have the Haynes book that has several partial diagrams, but I could not find one that includes the battery, starter/generator and the charging circuit.

    Also, in my prius there are extra cables to the battery on both the red and black side. I am guessing these are for the Defa. In a standard Gen 1, there is just a thick read and a thick black one?
  9. usnavystgc

    usnavystgc Die Hard DIYer

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    I have not found a complete wiring diagram available for free online but, I heard that you can download any info you want at toyota tech info (techinfo.toyota.com) for a small fee (I believe about $15 USD). I would try to find out where the extra wires connected to the + and - posts on your battery go to and disconnect them for starters. If that fails, you can start pulling fuses as R-P says.

    I'm not envious of your situation (lol)
  10. anon61

    anon61 Junior Member

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    Thanks for the tip! Googling a bit I found that there is European equivalent at Toyota Service Information. It has the wiring diagram for NHW11.
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