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12v Battery Questions...

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by going red baby!, Jun 6, 2013.

  1. going red baby!

    going red baby! still a n00b

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    So... I accidentally left the dome light on for 2 days. When I tried to start the car it wouldn't start. The interior lights all worked, the dome light was still on when I went out, the hatch light worked. I tried to start it but it wouldn't go into ready mode. The light on the start button wouldn't turn green, only orange. I figured I would get a jump the next day. Well, I let it sit that day and went back out to it the following day, today, and it started. I was surprised. I took it on a short drive to run an errand - less than 2 miles - it started again to come home.

    So... how did it not start - seemingly due to a dead battery - then start a couple days later? Does the traction battery charge it at all if you can't get the car in ready mode? Perhaps I went temporarily stupid and forgot how to start the car properly the night I found out the dome light had been on and tried it? (not likely)

    How long should it take to drain the 12v if dome light is on? (both sides on)

    Do I need to get it tested? What if I never drive enough to fully charge it? I don't have any long trips planned and I don't have a garage to leave it parked in while in ready mode.

    Thanks!
     
    #1 going red baby!, Jun 6, 2013
  2. jdenenberg

    jdenenberg EE Professor

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    Your little 12v battery is a chemical device (Sealed Lead Acid, SLA, with the acid stored in an Absorbed Glass Mat, AGM). It can recover some energy while resting.
    No.
    Let's assume that the dome lights pull one amp. You have a battery that can store about 30 amp hours of energy when fully charged, so the dome lights will drain your battery in 15 to 24 hours (less if it is not fully charged) to the point where your Prius will not start reliably.
    The dealers tester almost always say that the battery is still good, so having them test it is a waste of money.
    The lead plates will become choked with sulfate crystals and your battery will die an early death.
    You can buy a Battery Minder and periodically plug in for a few hours to both desulfate the battery and safely charge it. See:

    Batteryminders Specials | BatteryMinders.com

    JeffD
     
    #2 jdenenberg, Jun 6, 2013
    kenoarto, going red baby! and jdcollins5 like this.
  3. going red baby!

    going red baby! still a n00b

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    Thank you so much! Very helpful. Now I have a bunch more questions...

    So I can use the Battery Minder by connecting it to where I would connect a battery I'm jumping from? Under the hood and not have to get to where the actual battery is? Can I test from there as well?

    Reading both BatteryMinder manual and car manual and it seems I connect to battery leaving connection to car intact? Prius manual says to disconnect the ground but doesn't show where that is in the picture.

    If I have to connect to battery itself and leave battery in the car to charge it, where should I connect the one that connects to the engine block or chassis? Maybe I do just connect under the hood? If I connect directly to battery do I leave the hatch open? Or should I leave the windows open and close the hatch? I don't really want the hatch light on but I've read that there might be some gas or something from battery.

    The cord is only 2' long according to description. They give all kinds of warnings about using extension cords that are freaking me out. I have those heavy duty orange ones from Home Depot, is that okay? I may be able to put my car in my neighbor's garage to use her outlet, leaving garage door open, but not sure.

    Lastly, how urgent is it to get the battery charged again? I can order through Amazon and get it tomorrow for $94 or I can get it Saturday for $90 or I can order from VDC and get it in 8 days for $99 which includes a free Digital Multi-Meter. Do I need that?
     
    #3 going red baby!, Jun 6, 2013
  4. jdenenberg

    jdenenberg EE Professor

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    Disconnecting the ground is to play it safe as the pulsed desulfation function may disturb the Prius electronics. The ground is the negative lead from the 12v battery to the car body. It is easy to install a switch in that lead, but use contacts rated at 30 amps and when you disconnect the battery, you will lose your radio presets and maybe the auto open/close on the driver's window - both are easily reestablished.
    Again, the negative lead is the one to the car body so you can attach the charger above the switch (near side to the battery). There is a disconnect cord sold at amazon for the 12vside of the charger which may solve your extension cord issue below - see the others bought list. I would just run the cord out a rear window and close the hatch.
    As the unit will break up any sulfation that has formed, there is no real urgency. Just take your Prius for a road trip to get it charged up a bit (full charging can take hours that way). Good luck,

    JeffD
     
    #4 jdenenberg, Jun 6, 2013
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  5. going red baby!

    going red baby! still a n00b

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    Thanks again Jeff!

    So I'm making my purchase and hopefully I won't have any more questions. The only thing I'm not sure of is the disconnecting of the ground on the Prius, but I haven't looked at it yet since I have the hatch full of stuff atm. Should I just disconnect the whole negative side of the battery? Oops, there's a question...

    Found the pic below in another post. So where do I connect the negative from the BatteryMinder? Is it okay to connect it to that metal ring outside the battery area? Or is that metal on the far side towards the left that it can be connected to, the thing that has the hole in it? Not sure what you meant by "switch". Then I guess I have to open the hatch from inside (don't know where latch is inside)? Or I guess I can get the battery back in from inside the car.

    Okay, now I found a pdf saying that the battery should be removed from the car to charge it. I attached it. I don't know what to do... I don't need the extension if I do that though, and if I'm going to disconnect it I might as well pull it out, right? If I do pull it out then do I attach both positive and negative to the battery terminals or do I still only attach the positive and ground the negative on something metal?

    Man, I used to replace batteries myself on my old '93 Toyota pickup but I'm much more nervous doing anything on this car.

    [​IMG]
     

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    #5 going red baby!, Jun 7, 2013
  6. jdenenberg

    jdenenberg EE Professor

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    Once you disconnect one of the battery cables (we are suggesting the negative cable to the car body as it is the easy one), connecting the charger is safe. One of your earlier questions stated a concern about out-gassing under charge, but the Battery Minder only does a slow charge so should not cause out-gassing and your battery is "Vented" (a vent tube from a pressure relief valve in the battery leads outside the car).

    The switch that I mentioned earlier would be a new component that you install in the negative connection to the car body for convenience. It would, along with the quick disconnect cable at Amazon, make connecting your Battery Minder easy to do.

    One last point. If you close the hatch with the battery disconnected, you will have difficulty reopening it. The hatch release is a 12v device. There is a manual release (crawl in through the rear seats), but that is a pain unless you are small. So don't close the hatch while 12v is disconnected.

    JeffD
     
    #6 jdenenberg, Jun 7, 2013
    going red baby! likes this.
  7. going red baby!

    going red baby! still a n00b

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    Okay, so...

    "negative cable to the car body" - so not the end on the battery... the other end? Haven't seen it up close yet. Gotta get to Goodwill and donate all those clothes sitting in the hatch so I can get to it!

    And as to switches, which is best? I did a search on Amazon and there's several different types:
    Amazon.com: battery switch: Automotive
    I figure I might as well get one if I'm going to periodically use the BatteryMinder to check and maintain the battery.
     
    #7 going red baby!, Jun 7, 2013
  8. jdenenberg

    jdenenberg EE Professor

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    The Hella looks like a good one, but you will have to drill a mounting hole in the hatch space for it.
    You will see where the negative cable attaches to the body when you take out the hatch cover and tool bin.

    JeffD
     
    #8 jdenenberg, Jun 7, 2013
    going red baby! likes this.
  9. Mendel Leisk

    Mendel Leisk Senior Member

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    I've hooked ours up to a charger many times whiles it's in the car and hooked up, no problems. I connect at the jumpstart terminal, in the underhood fuse box.
     
    #9 Mendel Leisk, Jun 7, 2013
  10. Bill Norton

    Bill Norton Senior Member

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    The Batteryminder brand has that 'desulfation' function that puts out weird AC voltage into the battery.
    Quote:
    • Patented full time pulse-type desulfation keeps battery free of sulfate or dissolves sulfate completely in older batteries
    That part scares me. I personally wouldn't use it while the connected to the car.
    I like the idea of battery switch and a power tap for the charger. If you had that setup and used the Batteryminder overnight once a week or so, you'd probably have a really long life LV battery.

    I'm not that into it..
    When I hook mine up I'll just disconnect the Neg battery cable and let it do its thing once in a while when I know I'm not going anywhere for a day or so.
     
    #10 Bill Norton, Jun 8, 2013
  11. Mendel Leisk

    Mendel Leisk Senior Member

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    I'm using a CTEK 3300, that does a desulphation phase, no problems. One time I left it hooked up for a couple of weeks, while we were out of town.
     
    #11 Mendel Leisk, Jun 8, 2013
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