https://en.wikipedia.org/wiki/Hydrogen_sulfide#Incidents
In June 2016, a mother and her daughter were found deceased in their still-running 2006 Porsche Cayenne SUV against a guardrail on Florida’s Turnpike, initially thought to be victims of carbon monoxide poisoning.[65][66] Their deaths remained unexplained as the medical examiner waited for results of toxicology tests on the victims,[67] until urine tests revealed that hydrogen sulfide was the cause of death. A report from the Orange-Osceola Medical Examiner’s Office indicated that toxic fumes came from the Porsche’s starter battery, located under the front passenger seat.[68][69]
Yikes! I owned a late 1980s Mitsubishi SUV that had the battery under the driver's seat. I had to flip over the seat and remove a hatch to access the battery. The insulation wasn't very good. About 20 years ago I donated it when the battery couldn't keep a charge and the engine was having problems. To think that battery fumes could have done me in is scary. All my other cars have the battery far away from the passenger area.