well, since they suggest it is rs485, I would use a max3485 connected to the esp and connect that to the BMS. I opened the bms to check the chips inside, but all I could find by quick check is 122U31 chips, which are digital isolators. So the internal processor probably speaks modbus directly at 3.3V TTL level and the additional RS485 module that can be bought is just a simple converter with a max3485 and step down voltage converter to expose a rs485 signal. I am building a test setup with 14s1p, the bms and an esp-link and will see if I get it working with or without the rs3485 converterI'm confused on why you think I should be using a converter - what kind of a converter?
I plug my wifi adapter directly into the uart port of the BMS.