It is £4000 for a new replacement and you can't get it from anywhere other than the dealer.
He was complaining that he was utterly reliant on the dealer for repairs.
That would mean whole Inverter module (cars use same electronic that drives motor for charging), in that case new dealer £4000 price starts making some (but not a lot as I assume car still drives thus the expensive bits are working) sense. Still should be able to source something second hand if car is not under warranty.
Generally. I've had issues with electronic modules that need to be re-coded and can only be done at the dealer.
I've had a light cluster that would be a few thousand for a replacement after the ballast failed. The ballast failed after the sealed unit had water ingress due to the sealant (or whatever it was) failing between the light glass and the module body.
I sourced a second hand unit from a breaker but it needed to be coded to the computer. I sold the vehicle with the fault for as I didn't want to spend any more money fixing electrical faults (there were other previously).
The whole thing is built in a way where you cannot repair any of it and requires a dealer to be involved.
This is one of the reasons why I drive a vehicle that only has simple electronics now (my vehicle does not have an ECU) and generally avoid smart/IoT anything.