12v OEM—AGM or not

Discussion in 'Gen 3 Prius Technical Discussion' started by ryano7700, Jan 20, 2020.

  1. Grit

    Grit Senior Member

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    Someone bring a SLA battery to our next meetup, I will do a blind fold test.
     
  2. Elektroingenieur

    Elektroingenieur Senior Member

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    Yes. The handbooks for the Toyota Hybrid Systems (071) and Electrical Circuit Diagnosis (623) training courses, available by subscription to techinfo.toyota.com, mention 00544-21171-325 as an example of an AGM battery, in their discussions of auxiliary batteries for hybrid vehicles.

    Toyota’s battery application chart (PDF) confirms that the -325 part number is, in the U.S., the TrueStart replacement auxiliary (12 volt) battery for third-generation Prius cars. This was changed in 2012 from the original service part number, 28800-21171. The chart also now gives the JIS size, S46B24R.
    Alas, that’s not correct. It’s fourth-generation Prius and Prius Prime cars that use a conventional (flooded) lead-acid auxiliary battery, since it’s under the hood on those models. (The training courses I mentioned haven’t been updated to reflect this fact, by the way.)
     
  3. psusi

    psusi Junior Member

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    Yea, I call bull. Even if the battery were burning off a continuous 50 watts of power ( and that would get it quite hot and boil off the electrolyte quickly ), how much is that compared to driving? What's it take per mile of driving? At least 250 watt hours. Say you drive 100 miles over 3 hours. With 150 watt hours being wasted by the battery, that eats up only 0.6 miles of range on that trip. If you were getting 50 mpg with a good battery that means you were spending 2 gallons of gas to make that trip. With the bad battery you're now spending 2.012 gallons, and getting 49.7 mpg. Difference is well below the placebo threshold.
     
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  4. sam spade 2

    sam spade 2 Senior Member

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    AND that does not necessarily mean that an AGM would not be a better choice when it comes time for a replacement.

    I personally think that this is another case of doing something bad for the consumer just to save a couple of bucks in production.

    How many (first time) new car buyers these days even know that you might need to check the "water" level in a battery ?
    And how many of them know about using only distilled water ??

    Pretty close to none, I bet.
     
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  5. Mendel Leisk

    Mendel Leisk 'Orrible Oracle

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    In my experience, conventional battery water (aka electrolyte) levels didn't drop that fast. My rule-of-thumb over the years evolved to be: pull the battery out, about midway through it's life (say 3 years), clean the posts and cable clamps, check the levels (typically translucent case) by holding a light behind it, top up with distilled as needed.

    You could on the other hand, do nothing, and the battery might expire a little sooner, likely not much.
     
  6. sam spade 2

    sam spade 2 Senior Member

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    Where you live can have a BIG impact on the electrolyte level.

    New cars these days generally have lower charging voltages so actual electrolysis loss won't be as much........IF everything is working right.

    Ambient temperatures, however, will cause actual water evaporation losses.
    Where you live, that might not amount to much.
    But where I live, it can be significant.
    :)
     
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