Have you tried logging the Bluetooth protocol that is sent between the BMS and e.g. your phone with an ordinary Bluetooth sniffer/logger? I've heard, there are a few good sniffer out there and you might be able to see, what protocol the BMS BT adapter is actually using. As the Bluetooth adapter connects to the same port as the UART, I'd assume, at least the messages are the same. But no guarantee on that ...