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.
The vent system for the battery gases in the Porsche was not set up correctly, so instead of venting to the outside, they were venting inside. It was not a factory issue, but a replacement battery issue. Whoever replaced the battery used an incorrect battery and did not install it properly.
My brother’s 2015 Jeep has the battery under the passenger seat, but it is properly vented to the outside.
So those of you who have a battery inside your car, make sure it is the correct battery and if it requires venting, the the vent system is connected and working.