The battery is inside and sealed so the fumes from the battery would not normally effect the smarts battery post however if a car has been sitting and has a old battery it is possible that the battery has been recharged with a battery charger if the battery was overcharged and swollen up the battery case could be cracked which could lead to all kind of nasty things to happen.
This is why I mentioned checking that battery and connections plus the date on the battery. Most new cars come with a three year battery. but if it sits for along time this will shorten it life. its better to check these things out before you need to so there is no surprises. as the battery is just inches from the passengers feet. a defective battery that blows up can cause quite a bit of damage to the car and its occupants its much better to be safe than sorry.Batteries contain sulfuric acid and should not be taken lightly especially when the battery is so close to it occupants.
This is what happened to me while working with sulfuric acid. Note I was in a level B Hazmat suit at the time. and I still got burnt.
Keep in mind I had a Hazmat suit on and I was under a emergency shower only seconds after getting this on me. if your on the side of the road or in your garage without any protection the outcome will be much worse.
to this day I wear a beard to hide the scares.
Note do not look at this link if you dont like to see burnt skin.
Sulfuric acid burns pictures by Knelson1969 - Photobucket
I hope this is enough said about battery safety