Do we really need the12 V Battery vent?

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.

 

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

 

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.

 

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.

 

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

 

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.

 

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.

 

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.

 

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

Fitting mobility 12volt AGM battery. | PriusChat

 

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.

 

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.

 

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

 

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.

 

So.....what does that have to do with anything ??

 

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.

 

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