To vent or not to vent
Well, the headlights have been dimming noticeably at stop signs on my 2006 Dodge Charger. It is my experience that it is not worth it to get that last year out of a car battery (this is Minnesota and they tend to fail on Friday afternoon at work when it's cold as hell and you've had to stay late and everyone else has gone home).
So I replaced it.
This particular Charger (and all of the late model ones, Renaissance Chargers, if you will, to distinguish them from the 1960s muscle car era ones) has the battery in the trunk, under the cardboard I-want-to-be-a-carpet-when-I-grow-up liner, next to the spare tire. Mind you, Chargers of all eras famously have rear seat backs that fold down so that the trunk and the passenger compartment that are one and the same. Two can sleep (or whatever) in the combined space.
The battery isn't vented, in any meaningful way. Well, there's a little piece of 3/16" hose that goes through the sheet metal of the bottom of the trunk and connects to the battery.
I recall that, back in the day, Volkswagen beetles of the 1960s and 1970s placed the battery under the rear seat. There were no venting provisions whatsoever. The main concern at Volkswagon, was to provide an external sensor to measure the electrolyte level, so that the shop knew whether it was worth it to take the back seat apart to put in more water. (They had, at least in the 1970s, a precursor to the OBD port, in the form of a bazillion wire socket in the engine compartment, that connected to the battery level sensor and a couple dozen other places)
There is, as far as I know, no history of Volkswagon rear seats exploding. Or Charger trunks.