The CANdapter is necessary to connect the Orion BMS unit to a computer via a USB port to upload settings to the BMS, updating firmware and logging data to a PC.  One CANdapter can be used between multiple Orion BMS units and is only needed when settings need to be changed, firmware needs updating or if diagnostic data needs to be retrieved from the BMS unit.  

More info on the CANdapter can be found at