Last friday I smell a sulfur smell coming in the climate intake vents. A quick internet search said this was almost certainly the 12v battery, but being an electric car and fires being scary I took it to the closest dealer and Ubered home.
They said the smell was, indeed, coming from the 12V battery ($343 diagnostic, woot) and that it would be $550 to replace it. They also said,
The battery discharge warning is almost certainly the roadtop carplay adapter. Since I installed it, it displays things on the screen long after the car is "off".Recommend additional diagnosis of the electrical charging system after battery replacement.
Comments: There is a discharge battery warning coming on and additional diagnosis is recommended to verify new battery is not being over charged.
So, I ignored that part of the diag, bought a battery from the parts dept for $150, and replaced it myself in half an hour.
The battery I took out was HOT. As in, so hot that I couldn't touch it with my bare hands... and felt compelled to wear a face shield, in case it suddenly did something.
After replacing the battery, the sulfur smell is 100% gone. But, every time I start the car up for the first time, there is ~5 seconds of smelling every so slightly like burning plastic.
... think I should be concerned, and there is an overcharging issue going on? What might cause an overcharging of the 12v battery?