Intrude upon an H2S area and the eyes will sting. Yes, H2S is pervasive. Unlike straight hydrogen it does not tend to rise. Many bad batteries smell like sulfur. It's best to not chance it even though the production of H2S would be under a tenth of one percent of gas emissions.
Around batteries, eye and skin protection and first aid materials -at hand- are paramount. Heat battery acid to 150F. immerse a chunk of hamburger while dressed in HAZMAT suit. What you will see is guaranteed to leave a lasting memory.
RE: The battery in the car. If it degraded to the point that the car would not start that would have nipped the problem in the bud. Second point. If the vehicle had a runaway voltage regulator would not that model of vehicle have a fault announcement and revert to open loop limp home?
Maybe there is NOTHING wrong with the battery?
The individuals were found expired. The autopsy claimed H2S was the offender. Now it's CO that's a suspect. Not in blood but in urine. This stinks.