The hardware for the battery management system will fall into two types:
Temperature Measurement
Normally limited a few channels and points over a complete battery pack.
Voltage Measurement
Denso claim that their individual cell voltage measurement has an error within 3mV.
BMS Hardware Suppliers
There are a number of suppliers of BMS worldwide who design and build systems for single cell all the way up to complex managed BMS systems that can control very large grid based battery systems.