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12V battery reading low voltage

Discussion in 'Gen III 2010+ Prius Care, Maintenance and Troubles' started by Codyroo, Dec 21, 2011.

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  1. Codyroo

    Codyroo Senior Member

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    As the weather has gotten colder (32F +/-2F in the morning), my car is not going into ready mode as consistently as it was in warmer months. I also notice that I have a much better chance of success of going into ready mode if I let the car "pressurize" for about 10 seconds prior to pressing the power button (pressurizing = whatever is going on when you open the driver door and you hear the electric noise of something working (brake pressurization?) in the front of the car that runs for about 10 seconds).

    In a previous thread, my morning voltage (measured at the battery using a volt meter) was 10.4 volts (roughly 12 - 14 months ago).

    I've been looking at my voltage in the morning on my scangauge II, and the voltage this morning was 10.0 +/- 0.1 volts. When I hit the power button, the car didn't go to ready, and the voltage dropped to 8.8 to 8.9 volts. I hit the power button again and the car went to ready mode and the voltage was reading 14.6 volts.

    Driving the car on my commute, it will read 14.5 to 14.6 volts and when I shut the car down at work, the voltage is usually in the mid 12's (maybe low 13) volts. But will likely be in the low 10 volts tonight when I leave.

    Is it Optima time?
  2. KK6PD

    KK6PD _ . _ . / _ _ . _

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    This is the 4th thread about the same problem. Your 12 volt battery is SHOT!!!
    Do not pass go, do not collect $200, BUY a Yellow top Optima battery for the car. Think of it as a nice XMAS gift for the car!
    Optimas are easy to install, have better reserve capability, as opposed to more cranking Amps, wich you do not need in the Prius!
    They now make a version specificaly for the Prius! Read the following thread!

    http://priuschat.com/forums/prius-h...-12v-yellow-top-d51-battery-pencil-posts.html
    1 person likes this.
  3. fuzzy1

    fuzzy1 Senior Member

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    Think of it this way ... in a non-hybrid, that battery would have been dead last year. Your Prius is so efficient that it gave you more than an extra year's service out of that battery.

    Unfortunately, that year was not trouble free, and the trouble rate can only increase, at some point extremely rapidly. Unless you enjoy brinksmanship, give it up now.



    That is too high, the inverter is fighting to charge the effectively dead battery.


    Voltage immediately after shutdown doesn't matter much, its what's left the next day or week that counts.
    1 person likes this.
  4. Codyroo

    Codyroo Senior Member

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    I figured as much. At least I got another year out of the battery AND I'm in time to get the new Optima battery that will fit the car.

    Do you suppose my MPG's will increase since the car won't be trying to charge the 12V battery?
  5. pfjmarina

    pfjmarina Junior Member

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    So the 12 volt battery in the Gen III only lasts a couple of years? That seems pretty short compared to most conventional cars. What have other folks experienced as far as 12V battery life in the Gen III?
  6. DetPrius

    DetPrius Active Member

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    From the experience of others on this site, your MPG may very well increase. Have you noticed a drop in MPGs? Also, this is another 2010 with a SHOT battery, so, was the battery ever drained by accidentally leaving the lights on or from some other cause?
  7. Codyroo

    Codyroo Senior Member

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    When I first got the car, my son left the dome light on overnight. Why? Who knows. The battery was not dead and the car started up fine the next day. As far as MPG's, I've not noted a drop nor any other "unusual" events that are attributed to a dying 12V battery.

    However, it has had an intermittent problem with the battery not firing up the computer. I first noticed this when I had about 3700 miles on the car (2 months of ownership) and it has happened since.

    I think the battery came this way. While there was an event early on in its life, I don't believe a single drain (and not a full on, dead dead dead drain) would lead to the problems I've seen since May 2010.

    I could be wrong.

    Others have had similar issues with their OEM battery, which is why I've been monitoring it as frequently as I do. It has been surmised that Toyota got a bad batch of batteries and if this is true, it seems that I may have one as well.

    I've placed my order for my Optima and hopefully will have it before Xmas (or right after) and will have a new battery to usher in the new year.
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  8. Mendel Leisk

    Mendel Leisk Senior Member

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    With a regular car battery that's not so bad, borderline. Prius and similar (Civic Hybrid for example) come with 12 volts which are smaller than usual, since they're not used for starting (at least not typically: the Civic Hybrid has a conventional starter that is employed if it's very cold, or there's a problem with with the Hybrid battery).

    The Achilles heel of these batteries is they're very easily depleted: dome lights or map lights left on overnight can really "dent" them.

    A decent digital multimeter is one tool that can clear the clouds as to your battery's state of charge. Measure with the car off, and not immediately after recharging, since this will give artifically high readings. Anything around 12.6 volts measured thus is ok, higher say 12.7, 12.75, is better.

    And, just periodically for to keep the battery in-the-pink, or anytime you have an incident such as dome light left on, a lowish amperage intelligent charger session is warranted.

    A few proactive measures I take: switch the dome light completely OFF, so it doesn't come on when you open doors. D.O. for the hatch light. It is a minor incovenience, but the trade-off is you're much less likely to have accidental drainings.

    [​IMG]

    Just my 2 cents: when I replace our 12 volt I'll likely go with the same, OEM battery. They may be more vulnerable than a higher capacity aftermarket battery, but that's a non-issue if you are careful with them, and there's no fit issues.
  9. seilerts

    seilerts Battery Curmudgeon

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    The OEM is a starting battery with thin plates, while the Optima Yellowtop is a deep cycle battery with thick plates. Once drained, unless action is taken to trickle charge it to full immediately, the OEM battery will have chronic trouble. There is no fitment issue with the new Yellowtop. The only gripe I have is that they are not yet opening it up to other resellers.
  10. F8L

    F8L Protecting Habitat & AG Lands

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    The dealer could have depleted the battery before Cody even purchased the car. With enough people climbing in and out of the vehicle before his purchase I could see how the small battery could be abused. We've also heard of situations where the dealer purposefully let the battery run down while displaying a car on the show room floor then stating they will just recharge the battery later.
  11. Mendel Leisk

    Mendel Leisk Senior Member

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    Yeah, if it's an exact fit that's a non-issue. What do you mean by your last sentence: that it's only available via mail from Optima? Also, wasn't the price for the Optima more, close to double?

    I guess it all depends on your circumstances. If you're dilligent to avoid accidental drainage, the OEM will likely go the same distance, be more available, and cost you less (as long as you don't get stiffed on the install, do it yourself).

    OTOH, the Optima might pay for itself if you have an incident or two, and don't want to get into charging, voltage monitoring, etcetera.
  12. seilerts

    seilerts Battery Curmudgeon

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    The direct fit version, ds46b24r, is only sold by Optima directly, for MSRP of $199.99.

    Compare to the D51 Yellowtop, which also has an MSRP of $199.99 but sells online for $160+/-. If wholesale pricing for the ds46b24r were to mirror that of the D51, then places like Amazon and Elearnaid might sell the ds46b24r for $160+/- also.

    Demand will only increase, as there are over 1 million Prii on the road, and lots of people will want to go down to their local parts store and pick one up. I can't see Optima being the only seller of this battery forever.
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  13. Mendel Leisk

    Mendel Leisk Senior Member

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    So that's close to OEM:

    https://www.discounttoyotaparts.net/toyotapriusparts.html

    Thanks for the info ;)
  14. jdenenberg

    jdenenberg EE Professor

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    I just replaced the OE 12v battery in my 2004 Prius at 214k miles (after over 7 1/2 years and it still holds a charge!) with the new "Drop-In" Optima (I paid $170 for it using the offered coupon when it was introduced - the coupon is no longer available). I didn't bother to keep the 12v bus powered so I needed to reset the radio, clock, and auto window functions.

    One other problem occurred; the AC stopped working! [​IMG] The MFD said AC off and the steering wheel controls couldn't change temperature. It turned out that some of the electronics got out of sync. I noticed that the steering wheel controls for the defrosters still functioned so I hit the steering wheel AC mode switch which caused the MFD to say AC off. Then hitting the AC mode switch again got everything working again. [​IMG]

    JeffD
  15. itsnicetobe

    itsnicetobe Junior Member

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    I just bought a scan gauge II for my Prius and wonder what is a normal reading that I should have when I drive and start up the car. Also, what readings should I look for that would show a problem with the battery or charging system?
    Thanks
  16. jdenenberg

    jdenenberg EE Professor

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    Normal Prius 12v Readings:

    • Ready Mode - about 14v if noticeably higher, the charging system thinks that the battery is mostly discharged
    • Accessory Mode (no extra load) - About 12.4 volts if the battery is fully charged.
    • Accessory Mode (with extra load, e.g. headlights) still stays above 12v
    Things to look for as the 12v battery weakens:

    • Below 12v in ACC Mode
    • Lights on in ACC Mode and the voltage continues to noticeably drop
    • Voltage doesn't recover above 12v when load is reduced in ACC Mode
    JeffD
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  17. Codyroo

    Codyroo Senior Member

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    I received my battery and had it installed. The last battery was reading about 10.0 Volts (+/- 0.1 volts) on the scangauge when I tried to power up. This battery is reading 12.3 volts (+/- 0.1 volts) at start up.

    No issues so far.
    1 person likes this.
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