That being the VW Bug, but the entire VW line had batteries under the seat in those years, very handy spot too.No, in 40 years of being a gear head I've never heard of a single incident of a car battery exploding.
If you read the whole quote, I was saying that only a bad/over charge battery would went enough in the NON airtight space of a car to be an issue. MILLIONS of cars for DECADES have the batteries installed INSIDE the passenger compartment.
As a matter of fact, the highest production car on the planet, ever, has the batter under the rear seat behind the driver! Produced that way from the 1940s to the 1980s.
Is there always the 1 in a million exception? Sure! So its "Possible" but the "probability" of an issue, especially with modern batteries, is extremely low.
What was scary was where the aux gas heaters inside the bugs.
I have never seen a battery, any battery explode, saw one burn, but not explode. Did see an old lead acid that appeared to have blown up, the guy claimed it blew up, by blown up I mean the top busted open and side pushed out exposing plates, it was in a salvage yard and he nor I saw it blow, so something else may have caused that damage. I doubt it just blew up setting outside.