My fun story along these lines was with a 2018 M3 LR. After getting the car in September, in mid-May the SO got into the car, tried to start it, and Nothing Doing. Lots of alarms including Low Voltage.
Roadside assistance on the app invoked. Tow truck was there in about an hour with and tried to jump the car, no dice. Off to the SC they went.
This was on a Wednesday, I think. The SO was given a bunch of Uber credits, which she didn't use (I picked her up). Took until the following Tuesday for the diagnostics to get done, at which point she was given a Model S as a loaner. Tesla did remote troubleshooting and parts were ordered a day later; took until the following Monday for those to show, Tuesday for the work to begin, Wednesday they were done, Thursday we got the car.
Root cause: Short in the pagoda wiring harness blew the pyro fuse. That prevented the 12V from being charged, hence the low voltage complaints. They replaced the 12V battery while they were at it, I guess because it had been discharged to Zero. No problems with the car since then.
I'm a EE and mess with fuses, not huge ones, but the term, "Pyro Fuse" threw me, so I looked it up. It's kind of cool: When one has a short on the main battery voltage and the fuse blows, it's kind of important that the arc that forms where the fuse used to be gets quenched, otherwise, what's the point of a fuse? For those that don't know, an arc has a very low impedance. Not to mention that it gets, well, hot as the inside of a lightning bolt. The 350 V from the battery can throw quite an arc. The "Pyro" part of the fuse lights off a kind of firecracker that directs a serious blast of non-conductive gas across the fuse terminals, quenching the arc. At the time, the pyro fuse references I found pointed at a patent from Tesla, although I suspect that there may be other people making such things.
FWIW, I've known for a time that in city power high-tension wire switch gear yards, opening up a pair of contacts on a, say, 3000 volt high-tension circuit is not a job for the unwary. Back as an undergrad, the prof teaching a class I was in entertained us with the description of a blast of SF6 (sulfer hexafloride gas) from a bottle that gets let off as the switch gear opens, blowing the arc (as in, several feet of arc!) away from the contacts, SF6 having a higher breakdown voltage than mere O2-N2 air. After yea number of openings, they have to replace the SF6 bottle. Fun.
