Is vent mandatory for 12v battery?

My 12 volt doesn't have a vent on it...... Came from Autozone and cost close to $200 usa.

 

The vent will function ONLY in very unusual circumstances.......like a huge overcharging voltage or a really bad crash.
So no, as a practical matter, it is not "required" in normal operation.

Before you paid AutoZone $200, did you check with a Toyota dealer ?
Seems like I remember the price being a little less than that.......for some models.

 

depends on your safety comfort level. nothing is mandatory when you diy your own repairs

 

If you drive alone in your car, the lack of a vent only puts you at risk. (and as noted, it is rare to either create hydrogen gas or airborne sulfuric acid)

if you travel with others, you also putting them at risk.

Hydrogen - Wikipedia
Sulfuric acid - Wikipedia

Again, neither of these is likely if your voltage converter is working perfectly, but they are why the battery is vented.
As noted Hydrogen gas burns with an almost invisible flame. I watched folks in our HS chem lab set fire to their station without realizing it.
Thankfully I have no experience with sulfuric acid as an aerosol.

 

And whoever else is on the road or nearby. If you succumb to the gases while driving others would likely be at risk.

Since you are defeating a safety function you car insurance company could reject any liability.

 

This was 2 1/2 years ago and I was out of state traveling and my inverter went out. Didn't know what was wrong so tried a new 12 volt battery. I'll have to look at it again but don't get in there very often.

 

And again AGAIN:
An AGM battery does NOT release any harmful gasses except in the most extreme circumstances.
And there would be other indications to warn you.

Like many of your electrical system suddenly ceasing to work because they are fried by high voltage......OR hearing a loud bang and a crunching sound because your car has hit something hard.

 

Don't forget a potential third emission, even less common (indicative of a fairly serious electrical failure) but more toxic: hydrogen sulfide.