Brand new 12 volt battery not reaching 100% state of charge

Discussion in 'Gen 2 Prius Main Forum' started by GTW, Aug 7, 2018.

  1. GTW

    GTW Junior Member

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    I'm in my fourth month of ownership of a 2008 Prius Touring. I just replaced its12-volt battery with the highly recommended Yellow Top equivalent, specifically made for 'smart key' Prius. It physically fits perfectly, and has the vent hole on the side.

    The battery which came with the car (not OEM) displayed 11. 2 V (Prius Diagnostic mode - cold measurement). On advice received thru this forum, I replaced it. I have been driving with for a couple of days now, and the battery voltage from the cold measurement is usually about 12. 2 or 12. 1. According to a battery chart that I have seen here, that would indicate a state of charge of around 60 to 70%.

    Shouldn't a brand new 12V battery be holding a near 100% charge? Is there something on the charging circuit that I can take a closer look at? Thank you.
     
  2. TravisPrius86

    TravisPrius86 Junior Member

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    Take it for a long drive, see if that helps. Mine also stays around 11.2 in ACC and 13.5 driving
     
  3. dubit

    dubit Senior Member

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    In my opinion I'd say the battery is still ok - and that 100% charge your looking for will depend on how long the vehicle has sat, and how long of a commute you take. It may reach it, or it may never reach it.

    If it concerns you though I suppose you could get a battery tender.
     
  4. dolj

    dolj Senior Member

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    In my experience, a external battery charger is a requirement unless you drive several hours every day.

    Did you ensure the Yellowtop was fully charge before installing?

    BTW, for an AGM battery, 12.1 - 12. 2 V is ~37 - 43% SoC.
     
  5. Lucifer

    Lucifer Senior Member

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    Agree, trickle charge the new battery for a day, unhooked from the car.

    What battery, a yellow top equivalent...
     
  6. bisco

    bisco cookie crumbler

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    prius is virtually incapable of fully charging the battery. it is more of a maintainer. you need to start with a fully charged battery before installing.
     
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  7. sam spade 2

    sam spade 2 Senior Member

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    This.
    Most new batteries need an overnight charge before use and the onboard charging system is designed to MAINTAIN a full charge and might not be able to recover a full charge if the battery gets near dead.......which your readings indicate that it is now.

    If it consistently sits at 12.1-12.2, you should be concerned......as something is not right.
    What is the voltage when the car is "running" ??

    P.S. Since the 12 V system does not actually run a conventional starter, once it gets "full" it should be easy to keep it there (around 90%).......and an external charger should not be needed unless it sits for weeks at a time.
     
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  8. GTW

    GTW Junior Member

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    Optima YellowTop
    Part Number: 8171-767
     
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  9. JC91006

    JC91006 Senior Member

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    How are you measuring the voltage?
     
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  10. GTW

    GTW Junior Member

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    That explains a lot. I purchased the battery thinking it would be ''almost' fully charged. Standard car batteries are, in my experience, ready for use from the time of purchase. So once again anything Prius is turning out to be a different learning curve!

    Thank you for this explaination, but this raises a new question.
    If I take the new Yellow Top to the auto parts store for a charge, will they have an issue with deep cycle AGM? Their charger is going to be set for lead acid batteries. Doesn't AGM require a different type of charging cycle? Thank you.
     
  11. GTW

    GTW Junior Member

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    At first, through the car's Diagnostic mode. After the reading increased only two tenths of a volt after an hour of driving, I metered it on the battery. Both the car and the direct meter were a tenth of a volt apart.
     
  12. JC91006

    JC91006 Senior Member

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    Fully charge the 12v battery and I think you'll be fine
     
  13. Mendel Leisk

    Mendel Leisk Cloud Watcher

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    Check the voltage of the battery first thing in the morning, with a decent quality digital multimeter. It's possible the replacement battery is a dud, but hard to say till you measure carefully. You should be seeing at least 12.6 volts, with a brand new battery in good shape.

    Did you buy it locally? Maybe the store has electronic load tester, can check it? For DIY, something like Solar BA5 (or BA7) is good to have.

    With a volt meter, you want to check after the car's rested overnight, after a charging session, or even after a good drive, it'll be up a bit, what they call "surface charge".

    FWIW, the Yellow Top is nothing special. I actually have one in ours, the price was good when I was shopping. But I've read they're somewhat high in Cold Cranking Amps, but fall short in Amp Hours. It's a bit over my head, but next time (if that happens), I have some other ideas.
     
  14. sam spade 2

    sam spade 2 Senior Member

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    NO not really.

    There is no good reason to have a "deep cycle" battery in a Prius.
    But it's too late now. It won't hurt anything.

    Now would be a really good time to invest in a small (2 to 4 amp) fully automatic battery maintainer.
    It might take a LONG time (like 24 hours maybe) to charge a mostly dead battery but it should work.
    They can be had for $35 or less.
     
  15. Mendel Leisk

    Mendel Leisk Cloud Watcher

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    My CTEK 4.3 charger does have a setting for coil-wound AGM's (Like the Optima Yellow Top), basically charging at a slightly higher voltage. You can charge using that setting, or the regular setting. And a regular (smart) charger will work fine as well.

    FWIW, we're coming up on 3 years with the Yellow Top now, and it's still like new, assessed with a Solar BA5. Still, I'm the poster boy for obsessive compulsive battery maintenance: we don't drive much, and on idle days I always hook up the CTEK 4.3, it cycles and stays on, till the car is next used.
     
  16. GTW

    GTW Junior Member

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    I noticed that certain things didn't work at that voltage (11.2), such as the preferences stored in the MFD, and the engine Immobilizer never indicated. After the new battery was in, I saw the 'flashing car' on the display for the first time. I had to look it up.

    Another change with the new battery, is that my fuel economy increased by a couple of mpg (40 vs. 37). Didn't mind that surprise. Thanks for your feedback.
     
  17. GTW

    GTW Junior Member

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    Thank you for that recommendation. I'm shopping for one now. BTW, does the charger connect directly to battery, or thru the jumper contacts under the hood?
     
    #17 GTW, Aug 7, 2018
    Last edited: Aug 7, 2018
  18. PriusCamper

    PriusCamper Senior Member

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    Wow... So many comments in just a day... Back in the 90's Yellow top Optima's were the very best, especially among the car stereo crowd, but they sold out and their battery plant moved to Mexico and they've been making total garbage batteries ever since.

    One of the sales reps is on Prius Chat and he's blatantly admitted than when people return defective 12 volts batteries that don't hold a charge they just charge 'em up and sell 'em as brand new without even investigating why the battery is broken because they always think the customer is wrong not them.

    Get your money back and buy a real battery! If we had consumer protection laws the indictments against this corrupt company would of been handed down long ago and they'd be out of business entirely by now!

    Because Prius 12volts don't need cold-cranking amps to turn over an engine starter like regular cars, the primary function of the 12volt is equivalent to a back-up home power supply battery to power computers. So YellowTop can get away with selling garbage to Prius owners and they're non the wiser. But try jump starting a big old V8 engine with your Yellow top battery and the starter will barely turn over.

    The best 12 volt with near double the AMP hours of the recommended replacement battery is the most common battery that stores like Batteries Plus sells for wheelchairs and backup power supplies and because they seel so many, they only cost ~ $130. You have to add longer bolts and bushings to get the terminals to connect properly, but that's pretty easy to figure out. And most important, they sell so many of these batteries you'll never run into a problem like an Optima that's been sitting on a shelf for years because anyone who knows about batteries wouldn't spend a penny on that junk!
     
  19. GTW

    GTW Junior Member

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    I shopped around a little, and found the Yellow Top was in the middle of the price point. An AutoZone equivalent was $50 less, and the OEM was $50 more. I do know my brother has only bought Yellow Tops for his pick up trucks, and had been happy with them.
     
  20. PriusCamper

    PriusCamper Senior Member

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    Here's the truth with lots of links to the complaints too:

    "This company, retained several nationwide unsatisfactory records with the bbb for failing to respond to consumer complaints (links below).

    Along with having been issued 19 individual violations from the state enforcement agency, 'consumer affairs' (bar).

    Specifically, but not limited to, violating several sections of the business and professions code depicted below:

    Section 9884.7 (a)(1) false and misleading statements
    Section 9884.8 invoice requirements
    Section 988.4.9 (a) estimate requirements
    Section 3373 inserting/withholding info to cause document to be false/misleading"
    Defective Optima Batteries, www.optimabatteries.com - Defective made in China, Review 97327 | Complaints Board
     
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