Normally, it would be easy for the dealer to extract the individual cell-voltage values, which should tell a lot. If the battery pack is the cause, least one cell-pair must have a low voltage. Of course, there needs to be enough CAN buss function still active to be able to get the data.
A Black Box function, writing debud and status data to a high-capacity SD card would give readable diagnostic data even if the car's systems were no longer operative. Perhaps 10 minutes of each-second data, 10 hours of each-minute data, and 30 days of each-hour data would be helpful.
Computer unresponsive: needed to disconnect 12v to reboot.
Sudden loss of apparent remaining range: cause & fix unknown
Cannot turn car Off: cause & fix unknown
These could all be signs of software, firmware, or OS "confusion", which could be difficult to reproduce, but might be "cured" (for now) with a full reboot.