As above, if you connect anything directly to the battery negative terminal you will upset the battery monitoring system.
My useless local dealer did that with the battery maintainer whilst servicing my car, despite VIDA instructions to the contrary, and start/stop was unavailable when I picked it up. According to VIDA, the BMS should resync if the car is left parked and all doors shut and locked for 6 hours. I found that start/stop was working again the following day after the car had been parked overnight, but it's easier to just avoid the issue!
My useless local dealer did that with the battery maintainer whilst servicing my car, despite VIDA instructions to the contrary, and start/stop was unavailable when I picked it up. According to VIDA, the BMS should resync if the car is left parked and all doors shut and locked for 6 hours. I found that start/stop was working again the following day after the car had been parked overnight, but it's easier to just avoid the issue!