Do we really need the12 V Battery vent?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Paul Braathen, Jan 26, 2018.

  1. Paul Braathen

    Paul Braathen New Member

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    I had a replacement 12V auxiliary battery fitted yesterday, and I note that the battery supplied (Platinum
    BATTERY 043E 3YR/ 410A (SAE) had no visible vent hole, and therefore the vent pipe was left adrift.

    I was aware that the original S46B24R was an AGM and that the replacement would be a standard LA battery, but I expected that the supplier would at least fit a battery to accommodate the vent tube.

    Having expressed my concerns due to a possible build up of gasses expelled from the battery over time, given the positioning of the battery, I have been assured by both the supplier, and the battery manufacturer, that the vent tube is not required, and that Toyota no longer fit AGM batteries.

    Common sense tells me that a vent pipe to remove any gas (no matter how little there may be) is necessary, and I am sure that the supplier is only going on the information provided by the manufacturer.

    Therefore I would appreciate some confirmation, that either I am being overly concerned, or that the manufacturer is in error.
     
  2. Prodigyplace

    Prodigyplace Senior Member

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    Yes, you need the battery vent for Gen 2 & 3. Otherwise the Hydrogen gas escaping due to charging can enter the passenger compartment.
    You do not want Hydrogen in the passenger compartment!
    Your expectations are correct. I would get it replaced with a properly vented battery.
     
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  3. milkman44

    milkman44 Active Member

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    I replaced my 12V three years and three months ago with a sealed AGM deep cycle battery and no vent and can be used in any position and nothing leaks out. I've read here that the 12V is only charged at 4.5 amp, not like a 90 amp alternator is pumping juice to it. The AGM batteries in the motorized wheel chairs are charged indoors with no vent. If you will feel better, get the Toyota replacement for about $200, but for me this one is working fine.

    UPG 12V 35AH Group U1 Deep Cycle Sealed Battery | eBay
     
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  4. Grit

    Grit Senior Member

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    Not a work around but I drive windows down and sunroof open 99 out of 100 times and solar vent running when sunny, will it NOT be a health hazard to install and keep a battery like this that emits gas under those conditions? Thanks.
     
  5. Sam Spade

    Sam Spade Senior Member

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    Totally wrong.

    An AGM battery does NOT release any gasses during normal operation.
    The ones with vents on them are there just incase the charging system goes bonkers and WAY overcharges it.

    And hydrogen gas is NOT harmful......unless the concentration is high enough to become explosive or to push out all the air.
    Neither of those things is likely to happen with a tiny little battery in the Prius.

    The part that doesn't make sense in the original post is that he thinks he has a conventional wet cell battery with no vent.
    I believe that it probably really is an AGM and he should not worry.
     
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  6. ChapmanF

    ChapmanF Senior Member

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    Nothing leaks and no vent is needed when everything is going right, but you could say the same about airbags, or smoke detectors at home.

    There's a difference between "should be charged at" and "is charged at". The 4.5 amp figure is in the manuals (and a label on the battery itself) as a recommendation for when you have control of the charge.

    Gen 3 (and Gen 2 and Gen 1) do not have (much) current sensing on the battery leads. Gen 1 and Gen 2 have an independent remote battery voltage sense wire, which you could think of as a crude current measurement if you think of the main battery cable and fuse links as a shunt, but I doubt it's an accurate enough "shunt" for them to use it that way, and suspect they are just doing essentially constant-voltage charging. Gen 3 still has the same remote sense lead from the converter and doesn't even use it—they terminate it at a +12 junction within inches of the converter—but they have added a temperature sensor hanging in the air an inch above the battery.

    Upshot: 4.5 amps is a good rate for charging the battery, but I have never seen anyone on PriusChat post a measurement from a clamp meter of what's seen in practice, particularly when the battery charge is low.

    There's been a persistent PriusChat rumor about faulty aux batteries causing large drops in MPG, and many of its adherents propose much-higher-charge-current-drawn as an explanation for how that could be, but I have yet to see anyone who thinks that's the problem they're having put a clamp meter on and post the result.

    -Chap
     
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  7. Paul Braathen

    Paul Braathen New Member

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    I was quoted several prices here in the UK for an AGM battery replacement, from £260 down to £149. Knowing that the Aux battery has a fairly easy life, I also explored cheaper non AMG batteries, and found a standard VARTA LA battery (with an appropriate vent) which other Prius users had fitted at £56. Toyota actually quoted £120 including fitting, which I thought was quite reasonable. But then ATS came back with a quote of £80 inc fitting, and assurances that this battery was suitable. At £80 I got what I expected a standard LA, but no visible vent hole.

    I know it's penny pinching opting for a standard LA, but with so many users claiming about a 4 year life span on the Aux battery, it seemed unwise to spend more than necessary.
     
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  8. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    Your battery is very near the rear of the car, a minor fender bender is going to crack it open and expels sulfuric acid into the passenger compartment. AGM minimizes the amount of acid. It is simply a safety feature for humans.

    Same with the vent tube, burning hydrogen is hot. You are protecting humans.

    If no humans but you ever ride in the car, go for it.
     
  9. Sam Spade

    Sam Spade Senior Member

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    It is worse than penny pinching.
    I hope that you understand that you MUST check the electrolyte level in that battery, at least every 90 days and add water as needed.
    If you do NOT, the expected life might be MUCH less than 4 years and will erase any savings that you think you got.
     
  10. RobH

    RobH Senior Member

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    The VW beetle that my wife bought new in 1970 is still in daily use by our next door neighbor. I don't think AGM batteries existed then, so it uses an ordinary lead acid design. The battery is under the back seat. I couldn't tell you how many batteries have been in that car, but I can assure you that they didn't get the electrolyte level checked every 90 days. More likely the battery got checked when it no longer worked...

    Yeah, that battery design is dangerous by current standards. Compared to the rest of the vehicle, it barely makes the list of dangerous things. Airbags? Ha! Cookie cutter horn ring? Don't remember. Brakes? Sorta.

    I rather doubt that the electronics that charges the 12V battery in the Prius is even capable of putting out enough current to outgas it. That VW has a generator and voltage regulator that probably could fail. Inverters don't fail to overcurrent - they fail to zero output.

    If you have to chase every CYA warning, then you'll get a battery with a vent tube. Some of us have lived so dangerously that we've even used a ladder. Check out the warnings on new ladders at a hardware store. Scary.
     
  11. SFO

    SFO Senior Member

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    Read through this link, and tell us how concerned you are again :eek:

    Fitting mobility 12volt AGM battery. | PriusChat
     
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  12. Paul Braathen

    Paul Braathen New Member

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    Thanks guys, for all your input. I can see that some are as concerned as I was/am/should be, While others see the risks as large/small as they may be, as acceptable. I can see that (as my wife is the main driver), that my safest, while least expensive option, is to go for the Toyota £120
     
  13. LasVegasaurusRex

    LasVegasaurusRex Active Member

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    don't know where you're reading this but it's wrong. the 12v battery is babied by Toyota's hybrid system so they typically last about 8-12 years.
     
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  14. Paul Braathen

    Paul Braathen New Member

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    Thanks, that link is very interesting. It just makes me wonder why Toyota don't fit a battery that sounds perfect for the application. I suppose that if you make something too reliable, then you loose out on the servicing work :)
     
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  15. Andyprius1

    Andyprius1 Senior Member

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    I replaced the 12V with a smaller, around 30Ampere battery, no vent. Gen 2. If there is no vent there’s no place for H1 to escape to. Also there are 3-4 very sensitive shutter vents on each side of the car. These open easily when inside pressure exceeds outside pressure, eg: closing driver door. So any build up is constantly removed.
     
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  16. Andyprius1

    Andyprius1 Senior Member

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    Much of what Toyota does is overkill, especially the 12V battery.
     
  17. Andyprius1

    Andyprius1 Senior Member

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    It’s amazing how the price of a Auto 12 V battery has gone up. 20 years ago I paid $35, (lead acid) and now it’s $200 ! If the cost go up 5-6 times with the same life span, is it really an improvement? or just greed.
     
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  18. Sam Spade

    Sam Spade Senior Member

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    So.....what does that have to do with anything ??
     
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  19. Sam Spade

    Sam Spade Senior Member

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    Guess you haven't been keeping up with the battery problems reported on here.
    The weather (heat) and human owners and dealers do NOT baby the batteries, typically, so they often last only half of your estimate......or less.
     
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  20. Andyprius1

    Andyprius1 Senior Member

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    No electrolyte = no current = dead 12V = No Start!
     
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