Sounds like you have no idea how dangerous is to put your hands around electric car batteries and how expensive certified electricians are. Without a mechanic that ALSO has an advanced expert certification for high voltage electronics, the blown BMS or contactor (500$) becomes a whole battery to scrap (20k). Then you add the 6 hours of diagnostics and labor on top of it. Electric vehicles are not an arduino circuit with a couple of led and an usb cable.
This illustrates why the battery really needs to be decoupled from the car. We do it for other electrical appliances like flashlights. The EV auto mechanic should optimize for removing and installing the battery. Batteries should be taken offsite to a speciality facility where High Voltage experts work on the batteries - repair, recycling, etc.
It sounds like you are the one who has no idea.
There are a few basic things you have to not do in order to work on an EV, basically the same rules as for airbag systems but with physically larger components.
No modern car is electrically simple, but they all do a pretty good job telling you where you ought to be looking.
He is correct. If you have no idea what are you doing with BEV, you can destroy the car and your garage without even realizing what has just happened.
This is flatly false. The HV operating procedures on cars add significant complexity and danger to working on them. In fact, any HV work will automatically add a huge chunk of labor hours to any work and is why anything touching the HV system instantly goes into the thousands of dollars as a baseline. We are talking hundreds of volts above fatal baseline and very high amps on accidental discharge. For comparison, its safer on your biology to stick a fork in 120VAC outlet deliberately than to make a mistake with HVDC.