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time to change 12v?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by ramattos, Mar 13, 2015.

  1. ramattos

    ramattos Junior Member

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    ive noticed since getting the scangauge that while driving the voltage is constantly at 14.8 or 14.9. and when its off quickly drops below 12.5 after turned off.
    ive turned it off with the headlights and drops below 12 by the time the scangauge turns off.

    am i correct in assuming that its nearing the end of its life?
     
  2. phoenixgreg

    phoenixgreg Senior member

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    If it's the original 12 v battery on a 2010 - you've done well to get this far! Changing one out is not that bad, if you've ever done a car battery before.
     
  3. ramattos

    ramattos Junior Member

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    i did it on the gen 2 before i traded it in and it was a breeze.
    afaik it is the original one, havent had time to check date sticker.

    and is it normal that it is charging at such a high voltage? even after a 3 hr drive it never dropped below that.
     
    #3 ramattos, Mar 13, 2015
    Last edited by a moderator: Apr 5, 2015
  4. theotherone

    theotherone Junior Member

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    In general you can get an Optima Battery for about under $200 (including installation) at any local auto parts store (ie. Pep Boys). Toyota dealerships will charge you at least $300 for the battery & installation...
     
  5. AzWxGuy

    AzWxGuy Weather Guy

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    It is odd that there isn't more of a discussion about the 12 volt battery in the Gen III forum. Or maybe there is and I just haven't looked around enough. It is well covered in Gen II. And the assumption is that the systems and performance are similar.
    There are several methods to use to determine your 12 volt battery health. The first is age, and typically a battery will provide about 4 years of service. Some longer, some shorter. If you have ever left a light on or drawn the battery down to the point of needing a jump, then capacity should be suspect.
    The next step is to measure the resting voltage of your battery. It should be tested ideally after sitting overnight. Use a DVOM (digital volt-ohm meter) and measure the voltage at either the jump point under the hood or at the battery in the right rear corner of the car. A voltage of 12.0 or higher is usually good. Some will say the voltage should not be less than 12.5 volts.
    There is a procedure mentioned extensively in the Gen II forum that uses a built-in feature of the Prius to indicate 12 volt battery voltage on the MFD screen. In the Gen III you get to this screen by first going into ACC mode (one press of power button WITHOUT foot on brake) and then press and hold the INFO button on the right side of the MFD screen while rotating the headlight switch to parking lights and off three times. Then make on-screen selections of Function Check/Setting and then Vehicle Signal. When doing this with a Gen II, the first displayed voltage was a somewhat unloaded measurement. You wanted this to be 12.0 or better. Then you pressed the power button again to put the battery under a load. A brief drop below 12.0 volts was acceptable, but a static value below 12.0 was not good. Then you put your foot on the brake and pressed the power button again to make the Prius ready and read the charging voltage which was usually 13.8 to 14.5 volts. I don't think in the Gen III you get an unloaded measurement at the first reading. I just checked mine yesterday and the first measurement on the MFD screen was 11.5 volts and a subsequent DVOM measurement out under the hood was 12.69 volts. So that first measurement must be a little more loaded than it was in the Gen II. I do hear my navigation DVD spin up and there are perhaps some other systems activated too.
    This is pretty much all I know about it at the moment.
     
    #5 AzWxGuy, Mar 15, 2015
    Last edited: Mar 18, 2015
  6. Danger

    Danger Member

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    I'm in the same boat also. I have a 2010 and never had a problem with start up or anything. But just for a piece of mind I will look for a replacement battery.
     
  7. qdllc

    qdllc Senior Member

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    My universal test for failing battery has always been headlight intensity. Some of you know what I mean. If your headlights dim when you come to a stop, it means your 12v battery is failing because the car is using the alternator output to get up to full power once you start moving.

    However, the Prius is set up different, so I'd not expect you get any warning sign like that. Why doesn't the Prius have a "low battery" warning when it senses the 12v is under X volts at startup (something it should never be if in good condition)?
     
  8. Mendel Leisk

    Mendel Leisk Senior Member

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    Our resting voltage has been slip-sliding a bit. These days around 12.4'ish. The battery was put in, brand new, Nov 2010 when we purchased, so will be 5 years in the car come Nov this year. Never had a accidental drainage, knock on wood. 'Course I keep the dome light right off, same for hatch light. My son thinks I'm nuts, lol. I might replace ours this fall, just bite the bullet.
     
  9. RRxing

    RRxing Senior Member

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    Here's the actual Toyota procedure...
     

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  10. Preeeus

    Preeeus Member

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    [QUOTE="AzWxGuy, post: 2152875, member: 76845"...I don't think in the Gen III you get an unloaded measurement at the first reading. I just checked mine yesterday and the first measurement on the MFD screen was 11.5 volts and a subsequent DVOM measurement out under the hood was 12.69 volts. So that first measurement must be a little more loaded than it was in the Gen II. I do hear my navigation DVD spin up and there are perhaps some other systems activated too.[/QUOTE]

    Hmmm... our 2010 (with nav) got a "P Lock Malfunction" error the other day ("P Lock Malfunction when parking, park in flat place and apply parking brake securely."). We checked the battery voltage via the MFD screen with the car off (one press of the power button with no depress of the brake), and the level was 11.6V. Until reading your post, we thought we had it figured out that the 12V battery must be dying, causing the "P Lock Malfunction" error. After reading your post, we're not sure what to think.

    What's the consensus? It seems like everyone has been saying that any reading under 12V via the MFD is too low, but your post seems to indicate otherwise.
     
  11. bisco

    bisco cookie crumbler

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    the problem with the mfd method is, you have to fire everything up to get it. there is no 'unloaded' reading. best thing to do is unlatch the hood in the evening, open it in the morning and put a dvm on the charge post. my 3 year old battery reads 12.7 this way.

    great find, thanks. should be a sticky. there are a lot of people who think 12.0 and higher is just fine. that's a nice procedure for removing the surface charge, instead of waiting for it to dissipate.
     
    #11 bisco, Apr 5, 2015
    Last edited by a moderator: Apr 5, 2015
  12. lar.smith42

    lar.smith42 Active Member

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    passport05042015.jpg
     
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  13. Preeeus

    Preeeus Member

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    Lol... I wonder if I just toasted my DVM trying that!

    I put red to red and black to black, and... dang! those wires are hot!!!

    Then I took a close look at the DVM, and it says 10A max for DC (in tiny print). Ummm... I know these batteries have hundreds of CCA's... what does that translate to for normal Amps? Did I just fry my DVM?
     
  14. bisco

    bisco cookie crumbler

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    not positive, but i think it should handle it. mines a cheapo and works fine. if it's fried, you needed a new one anyway.
     
  15. Preeeus

    Preeeus Member

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    Lol... I think it may still work (have to try it out on some known items), but the wires got hot real fast, and it read 0.00, so I removed the leads before my hands melted.


    Does the Optima Batteries 8171-767-FFP (DS46B24R) YellowTop Prius Battery available on Amazon ($147.05) require any special adapters or hardware for installation on a 2010 Prius (gen III)? Some people claim it requires a kit, like the one from eLearnAid, other people say it's a direct drop-in. What's the story?
     
    #15 Preeeus, Apr 5, 2015
    Last edited by a moderator: Apr 5, 2015
  16. CR94

    CR94 Senior Member

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    You must've had your meter set on an ampere (current) scale, or had the red lead plugged into a specific 10A socket (which some meters have). Try using an appropriate voltage scale (and socket, if applicable) and those wires will not get hot at all.
     
    #16 CR94, Apr 5, 2015
    Last edited: Apr 7, 2015
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  17. gliderman

    gliderman Active Member

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    Most meters have a fuse in them. You can change the fuse.
     
  18. bisco

    bisco cookie crumbler

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    i know optima has the correct battery for the gen III, i don't know if that's it or not. the kits were when they first came out, they didn't have the same post size. you can contact optima directly, or pm member optimajim.
     
  19. Preeeus

    Preeeus Member

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    Hmmm... I had it set on DC V, with the selector switch set to 20V (the options are 200m, 2000m, 20, 200, 1000), the red lead connected to the 10ADC socket (the other socket is 200mADC), and the black lead connected to "Common". Is that correct?

    I don't think the fuse blew, because it still turns on.
     
  20. macman408

    macman408 Electron Guidance Counselor

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    Don't even bother with the voltage from the car's own reading. I checked mine with a multimeter once; when the service menu said 11.5V, the multimeter under the hood read 12.2V. Another member got 11.2V on the service menu and 12.75V under the hood. So it's not even *consistently* wrong across cars. It's just a horribly inaccurate sensor.

    I would get worried if you measure <12V with a multimeter and no load (i.e. everything off, all doors closed, and key far from the car, >1 hour since it was last used). Others are a little more anal, and say things like "Oh god, if it's below 12.7V, it's on its last legs! Run for the hills!" My battery has measured 12.5V pretty consistently since I got the car 5 years ago. No signs of needing replacement yet...

    That was probably not correct, at least if your meter is similar to the ones I have/use. On those, the 10A socket is only for current measurements, while the low-current socket (in my case, 400 mA) is for low-current measurements AND all other types of measurements (frequency, voltage, resistance, capacitance, etc.). The 10A socket is designed for very low resistance, so unlike the other socket, it'll probably let lots of current through even if it's just in voltage mode.

    The fuse is in line with the socket, not with the power to the multimeter. So if you were to try to measure current, it would just read 0 because the fuse has blown; blowing the fuse won't keep it from powering the meter on. The other socket has a separate fuse, so it should still work.

    Anybody who has spent any significant amount of time with a multimeter has probably done something stupid with it at some point - like accidentally measuring the current capability (instead of the voltage) of a wall socket (HINT: It's a lot!), or shorting two different circuits together with one of the probes. (I'm guilty of the latter, when working on a circuit board a number of years ago. I don't even know what I shorted, but a surface-mount tantalum capacitor on the board exploded and shot off a nice 4-inch flame. I unplugged the power, blew out the flame, and the capacitor kept glowing white hot for a few seconds. I'm assuming I must've shorted something, because those capacitors are particularly sensitive to having reverse voltage applied.)
     
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