The hardware for the battery management system will fall into two types:

Master and Slaves: a slave will monitor and control a sub-set/module of cells and communicate back to the master.
Centralised Control Unit: long leads are required to connect the central control unit to every cell in the pack.

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.